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alexandraerinUnder the theory that more eyes are better than fewer, I've decided to post the draft of my abstract combat system for D&D. This system owes a debt of inspiration to the "SARN-FU" system (detailed here), for showing me a good model for handling abstract distances. My original plan was to use SARN-FU, but I had a few issues with it:
While I started out just adding rules for blasts/bursts and forced movement stunts to SARN-FU, when I was finished the only thing it had in common was the basic idea of using relative distances, so a new name (and better acronym) seemed to be in order.
This has not been playtested. It has not even been thoroughly checked by anyone who isn't me.
THE ACME SYSTEM
The Abstract Combat Mapless Encounter system, or ACME system, is an unofficial "add on" system for 4th Edition Dungeons and Dragons. While I believe that the rich combat experience D&D is best enjoyed with map tiles and miniatures of some kind, there are some situations in which a more stripped down and imagination-based approach works better. Online games, for instance, can bog down if not everybody has a system or connection that can handle the map tools. An abstract game can be played with fewer materials and in environments such as a moving vehicle.
It's recommended that the DM at least has a notepad (analog or digital) to keep track of rough positions. Simple maps or room diagrams may still be useful for conveying the layout of a room, but aren't necessary. A whiteboard may be useful for keeping track of the combatants and their clusters.
The goals of the ACME system are as follows:
1. To provide a quick and simple way to represent relative distances between characters and determine who is within the area of an attack without using a map.
2. To allow every character class to fulfill its role as normally as possible during an abstract combat.
3. To make sure that every power and ability, even those that rely heavily on movement and positioning, retains its usefulness.
Although this system needs thorough testing, I believe it represents a good start in moving towards those goals. It does require imagination, flexibility, and cooperation on the part of all participants. In the absence of a map with discrete, countable squares and absolute positions, the players and their plans are more at the mercy of the DM than ever. For the ACME system to work to its fullest, the DM has to regard a game of D&D... even the combat portions... as an exercise in cooperative storytelling, where the goal is not to thwart the players but to challenge them and see how they overcome those challenges.
The underlying rules of D&D are not changed. The ACME system is a new way of running combats, not a modification to the game as a whole. Characters are created as normal and the game plays exactly as normal until combat begins. At that point, instead of setting up a battlefield using tiles or a grid, the DM describes the scene and details the enemy combatants. Then initiative is rolled, and combat begins... almost as normal. The differences are outlined below.
The rules below don't cover every case that could come up, but other situations should be adjudicated in keeping with the goals above. In particular, any power/ability should be interpreted so that it remains useful. For instance, if you're given the opportunity to remove a certain number of squares from the area of a blast or burst, you can use it to exclude that number of allies who are caught in it. If a player character has an ability which the DM feels absolutely cannot be translated into an abstract movement system, then the player should be allowed to "retro-train" it, swapping it out for something else.
DISTANCE AND MOVEMENT
This is the heart of the ACME system, the chief difference between regular tabletop play and abstract/mapless play.
DISTANCES
Distances on the notional "game board" are reduced to five basic levels. There are really seven, if you consider 0 (right on top of each other) and extreme far range (too far for magic missiles and long bows)... but the five listed below are the ones that will be dealt with the most often. These distances are all relative. A character can't simply be "adjacent" in general, but must be adjacent to someone. Both such adjacent characters might be near to a third, and the whole cluster of three characters might be at close range to a fourth.
Adjacent: The equivalent of right next to each other, one square over from each other.
Near: The equivalent of two squares over... i.e., with one square in between. All creatures who are either near or adjacent to you are "nearby".
Close Range: Roughly within five squares of each other. Anything in Close Range or nearer is "close by".
Far Range: Roughly within ten squares of each other. Combat usually starts with combatants this distance apart or closer.
Very Far Range: Roughly within twenty squares of each other.
CLUSTERS
A cluster refers to a group of characters that are bunched up around each other. At the start of an encounter, the PCs are usually in a cluster, unless they're deliberately spread out or have had time to move into specific positions on the field. They can decide if they're adjacent or near to each other. Their opponents will often be arranged in more than one cluster.
Clusters are not rigid and absolute divisions of characters. Members of a cluster may all be nearby each other (a dense cluster may have members that are standing adjacent), but a "cluster" is not a set unit of distance/width. Clusters are a tool for the DM to use in laying out the battlefield with some sense of space, as they allow enemies to be grouped closer to or farther from the PCs, or positioned at strategic or interesting points in the room. For PCs they provide tempting targets for burst and blast attacks and ways of engaging with smaller numbers of enemies at a time.
MOVING
If you're moving towards or away another character, then your movement speed is compared very roughly to the distance to determine how many move actions it will take (usually two to move from far range to adjacent, usually one to move from close range to adjacent or far range).
Tactics such as using a move action to move half the distance and then a standard action to charge the rest of it are still valid in the ACME system. Running, with its attendant bonuses and penalties, is the same as well. If it's important, exact movement speeds may be used to adjudicate tricky situations, i.e., if an enemy you just moved away from can catch up to you without running or charging.
If you don't want to approach an enemy head-on, to avoid dangerous terrain or traps, you can specify that you're "going around". This will eat up your movement at a rate determined by the DM. Feel free to discuss exactly what you're doing beforehand. Characters with higher than normal Move scores can expect a little more leeway, in relation to characters with lower Move scores.
FLANKING
Since the ACME system does not keep track of exact absolute positions, flanking can only be done intentionally, not simply by occupying space. You must shift into position while adjacent to an enemy to form a flank.
If you and an ally are both adjacent to the same enemy, you can spend a move action to shift and flank the enemy. This leads to both you and your ally having Combat Advantage against the enemy, as normal. Again, just moving adjacent to an enemy is not enough to form a flank. You must be able to shift after you're already adjacent, whether as part of another move action or as part of an action that lets you shift multiple times.
You cannot flank (or be used by an ally to form a flank) if you are flanked yourself. You must move to break the flank before you can shift to form a new one. You cannot be flanking multiple enemies at the same time.
BOXED IN
The boxed in condition represents the possibility of being truly surrounded, something that's easy to work out with a board and miniatures but somewhat harder to adjudicate in the abstract.
If more than one pair of enemies is flanking you, you are boxed in. While you are boxed in, you cannot move unless you teleport, fly, or use an ability that lets you move through an enemy's space or switch spaces with an enemy. You can also free yourself or be freed by ally, if you are able to shift or be slid x number of squares at once, with x being equal to the number of times you're flanked.
That is, if two pairs of enemies are flanking you, you need to be able to shift 2 squares or be slid 2 squares by an ally. This gets you free of all the flanks, though you're still adjacent to the enemies.
Alternatives to escaping from being boxed in may include situational uses of skills like Athletics or Acrobatics, or ending one of the flanks by defeating an enemy or pushing them away.
Creatures who are larger than Medium sized may require more flankers to be boxed in, at the DM's discretion.
DIFFICULT TERRAIN
The idea of difficult terrain works more or less as normal. Its position will usually be in relation to a cluster of NPCs: in front of them, or all around them.
If difficult terrain is between the PCs and a cluster of enemies, the DM should have an idea how much more movement it costs to go through it, or around. For encounter design purposes, it should usually take longer to go around, since the consequences of being caught on it (cannot shift) are worth avoiding.
FLIGHT
Flight functions as normal. The abstract distances may be vertical as well as horizontal. A character who is flying can usually bypass difficult terrain and non-flying guards.
TELEPORTATION
Teleportation works like normal movement in terms of getting closer or farther away from other characters. However, it lets you avoid Opportunity Attacks, bypass difficult terrain, and slip out of flanks without shifting. If you teleport adjacent to an enemy who is adjacent to an ally, you can create a flank (if such is otherwise possible) without shifting.
FORCED MOVEMENT
If you have a power that lets you push, pull, or slide another character, it's treated as normal movement. A push must move the target away from you and a pull must move them closer, as normal. A slide can do either. If you wish to do anything more fancy or elaborate, like knock an enemy off a cliff or into a fire, or slide an ally into a flanking position, or slide an enemy in between two allies to create a flank, you must make a check using the same attribute as the attack (or your class's primary attribute, if the power doesn't have one) with a bonus equal to the amount of forced movement to see if you can pull it off.
The DC is set by the DM, though it will usually be the Reflexes of the target if what you're trying to do is not conducive to the target's health. The DM is free to say that what you're trying is not possible. In general a slide will afford more freedom to be creative than a push or pull.
GUARDING
Guarding is a new mechanic for the ACME system, intended to represent the way a character can be positioned to block easy access to others. You can declare you are guarding one or two nearby allies by spending a move action, to represent getting into position. You remain guarding them as long as you are able to attack and until they are no longer nearby. While you are guarding, you grant them partial cover and anyone who comes directly towards them will pass by you, provoking an opportunity attack. You can also ready an action to attack the first enemy that approaches you.
Enemies can try to bypass your guard by using a move action to go around you. If they do not reach your allies on their turn, you can guard again on yours... using a new action to interpose yourself between the enemy and your allies once again. If enemies are approaching from more than one direction, you have to choose which approach to guard.
You cannot guard more than two allies at a time. You cannot guard an ally if you are being guarded... doing so ends the guard on you. Guarding requires your attention to be focused on your allies, so you cannot form a flank while guarding, and cannot guard while being flanked.
With the DM's permission, you can guard other things besides allies: a terrain feature or item, an enemy you don't want other enemies to reach, etc. No matter what you're guarding, you don't provide cover for anyone you don't want to.
ATTACKS
WHO CAN I TARGET?
Melee and Ranged attacks function more or less as normal. A melee attack with a range of 1 can only target adjacent creatures. If you have a "reach" attack or an attack with a range of 2, you can target nearby creatures. A range of 10 is sufficient to target any creatures out to far range, and 5 can target any creature out to close range. For other values, DM's discretion applies. With a shorter range (like 3), it may be necessary to spend a move action stepping closer without actually coming near to the target.
If your power targets one, two, or three creatures (whether enemies or allies) within a close burst, or targets all allies within a close burst, then it's resolved similarly: a burst 5 is sufficient to target anyone within Close Range, while a burst 10 can reach anyone out to Far Range. These powers often function more like Ranged attacks except for not provoking Opportunity Attacks
With Area, Bursts, and Blasts, things get more complicated. These attacks all target multiple squares on the battle mat, and often have the possibility of catching multiple enemies clustered together... or an ally who's too close.
CLOSE AND AREA BURST ATTACKS
If you have an attack that says "Close Burst x" or "Area Burst x in y squares" for the range, that burst includes all creatures who are adjacent to the origin of the attack (you, or the target within the indicated range if it's an area burst) if x is at least 1. If it's at least 2, then it targets all creatures who are nearby. And of course, the target of an Area attack is inside the burst.
After that, it's less certain.
Anybody who might possibly be within the burst and is a valid target of the attack is "threatened" by it. The DM rolls a d6 for each threatened creature. If the number is less than or equal to the size of the burst (x), then that creature is within the burst. For smaller bursts, this chance applies if a creature is clustered up around the origin. If the threatened creature is a minion, treat the burst size as 1 larger for resolving the threat.
Generally, creatures are threatened by a burst if they're in a cluster with the burst's target/origin. Depending on the size of the burst and exact situation, it's possible that others might be threatened. You can ask the DM who would be threatened before committing to the attack - in the real life being modeled by the game, you could at least eyeball it.
With Area Bursts, it's possible to target empty space in order to get clever and hit more enemies without hitting your allies. For instance, if two enemies are near to each other and you make one enemy the center of an Area Burst 1, you know you've missed the other and you need a threat roll for each of the others in the cluster. But by dropping an Area Burst 1 "in between" the two enemies, you know they're both effectively adjacent to the attack. That's two enemies who are definitely in the burst. This is a perfectly valid tactic when playing with a battle mat, and it remains viable in the ACME system.
Determining that a creature is in the burst only means that they're targeted by the attack. A hit roll is still needed to determine if they're affected. The rolling mechanic could slow down the game, which is why one person--the DM--rolls for everyone, in order to keep things moving.
In short: using bursts are good when enemies are in a cluster. If allies are fighting up close with those enemies, they may be caught in it.
Example #1: Scorching Burst is a Wizard spell that does an Area Burst 1 within 10 squares. The Wizard can cast it on any creature within Far Range. Any creatures known to be adjacent to the target are also caught within the burst, including the Wizard's own allies if they're engaged with it. If other enemies are in a cluster with the target, they might be caught in the burst, though there's only a 1 in 6 chance. This same possibility should be rolled for any allies who are adjacent to these enemies... they are in the cluster, too.
Example #2: A Kobold Dragonshield is guarding a Wyrmpriest. The Wizard decides to drop a Scorching Burst right between them. The two are both automatically caught in the burst. Any other kobolds who are in the same cluster might be caught in the burst... the DM rolls 1d6 for each of them.
CLOSE BLASTS
If you have an attack that says "Close Blast x" (usually 3 or 5), it's resolved a little differently. The ACME system makes use of a new mechanic, not present in the normal game. This is Wide Blasts and Narrow Blasts. You can choose to use either a Wide Blast or a Narrow Blast when you use the power. If you use a Narrow Blast, then you can target a number of nearby creatures equal to x. For instance, a Close Blast 3 power can target up to 3 nearby creatures with a Narrow Blast.
If that's not enough, you can use a Wide Blast. The Wide Blast lets you pick the same number of targets. Anyone else who is nearby or might possibly be caught in the blast is threatened by it. The threat is resolved exactly the same as for a burst, including the +1 chance for minions.
Flanking Limitation: Blasts are directional. You can't use them to scatter two opponents on opposite sides of you. Therefore, out of each pair of enemies that are flanking you, one member of the pair must be exempted from the blast. They can't be picked as targets. They cannot be randomly affected by a Wide Blast.
Example #1: A Wizard is being guarded by an ally, a Warden. A horde of minions threatens to overrun the pair. The Wizard uses Thunderwave, which does a Close Blast 3 attack. Not wishing to endanger the Warden, the Wizard makes it a Narrow Blast and targets only the three minions that are directly attacking the Wizard. The other minions aren't threatened, but neither is the Warden.
Example #2: A Ranger who is a Half-Elf is off alone, sniping enemies with a bow. A horde of minions break away and surround the Ranger. The Ranger uses Thunderwave as a Half-Elf Dilettante power. With no allies nearby, the Ranger uses a Wide Blast. Three of the minions are automatically included in the blast. The others are threatened, and will be affected on a roll of 4 (3 + 1) or lower on a d6.
The Wide/Narrow blast choice differs from ordinary play, but the effect is similar: when you have a board with an exact known position for allies and enemies, you can usually use a blast power conservatively to hit a small number of opponents and miss your allies, if you choose.
OPPORTUNITY ATTACKS
Opportunity Attacks are provoked by the same things as normal: if an enemy is adjacent to you and moves without shifting, or uses a ranged or area burst attack. If it seems like an enemy would reasonably be moving past your character (because it's fleeing and you're positioned inside a bottleneck, or you're hiding near its likely path), the DM may grant you an Opportunity Attack. If it seems really likely that an enemy would be passing by you, feel free to ask... but doing so every time an enemy moves on the off-chance that they're wandering close to you may be hazardous to character health.
Some Explanations, or What I Was Thinking:
It would be the DM's job to keep track of where everyone is and give an overview of the combat field every round. This should ideally be presented in a visual form that players can refer back to, rather than having to keep the whole battlefield in their head. My thought is that for an online game, I would describe the battlefield positions in a block of text and for an offline game I would list the clusters on a white board or a sheet of paper.
The change to flanking (that you can't flank while being flanked) is to keep the number of flanks going on at one time, since each one is something that has to be kept track of (unlike in a tabletop game, when you glance at the board and see that your opponent is flanked.) The flanking rules and boxing in rules together are designed to create a sense of a dynamic combat with warriors jockeying for position, as tends to happen in 4E tabletop games. They also give more meaningfulness to the "shift" mechanic, since so many powers allow free shifts.
Guarding is meant to allow Defenders to do their job without the game devolving to something even worse than "I shot you!"/"No, you didn't, you missed!" -- "I stood in your way!"/"No, you didn't!"
- The movement system is unnecessarily mathematical and precise. If things are abstract, let them be abstract. My system has more of a fudge factor when it comes to movement and distance.
- The flanking system (though refreshingly simple) seems like it would be brutal in combats with large numbers of enemies.
- I wanted to have clear guidelines for adjudicating bursts and blasts, to keep them from either being total DM Deathtraps ("Oh, too bad... you hit your entire party with a fireball. Again.") or laser-guided multiwarhead for the players ("I position my fireball so that it hits every Kobold but misses all of us.")
- Likewise, I wanted rules for doing interesting things with forced movement that didn't turn pushes and slides into the equivalent of a Green Lantern Power Ring.
While I started out just adding rules for blasts/bursts and forced movement stunts to SARN-FU, when I was finished the only thing it had in common was the basic idea of using relative distances, so a new name (and better acronym) seemed to be in order.
This has not been playtested. It has not even been thoroughly checked by anyone who isn't me.
THE ACME SYSTEM
The Abstract Combat Mapless Encounter system, or ACME system, is an unofficial "add on" system for 4th Edition Dungeons and Dragons. While I believe that the rich combat experience D&D is best enjoyed with map tiles and miniatures of some kind, there are some situations in which a more stripped down and imagination-based approach works better. Online games, for instance, can bog down if not everybody has a system or connection that can handle the map tools. An abstract game can be played with fewer materials and in environments such as a moving vehicle.
It's recommended that the DM at least has a notepad (analog or digital) to keep track of rough positions. Simple maps or room diagrams may still be useful for conveying the layout of a room, but aren't necessary. A whiteboard may be useful for keeping track of the combatants and their clusters.
The goals of the ACME system are as follows:
1. To provide a quick and simple way to represent relative distances between characters and determine who is within the area of an attack without using a map.
2. To allow every character class to fulfill its role as normally as possible during an abstract combat.
3. To make sure that every power and ability, even those that rely heavily on movement and positioning, retains its usefulness.
Although this system needs thorough testing, I believe it represents a good start in moving towards those goals. It does require imagination, flexibility, and cooperation on the part of all participants. In the absence of a map with discrete, countable squares and absolute positions, the players and their plans are more at the mercy of the DM than ever. For the ACME system to work to its fullest, the DM has to regard a game of D&D... even the combat portions... as an exercise in cooperative storytelling, where the goal is not to thwart the players but to challenge them and see how they overcome those challenges.
The underlying rules of D&D are not changed. The ACME system is a new way of running combats, not a modification to the game as a whole. Characters are created as normal and the game plays exactly as normal until combat begins. At that point, instead of setting up a battlefield using tiles or a grid, the DM describes the scene and details the enemy combatants. Then initiative is rolled, and combat begins... almost as normal. The differences are outlined below.
The rules below don't cover every case that could come up, but other situations should be adjudicated in keeping with the goals above. In particular, any power/ability should be interpreted so that it remains useful. For instance, if you're given the opportunity to remove a certain number of squares from the area of a blast or burst, you can use it to exclude that number of allies who are caught in it. If a player character has an ability which the DM feels absolutely cannot be translated into an abstract movement system, then the player should be allowed to "retro-train" it, swapping it out for something else.
DISTANCE AND MOVEMENT
This is the heart of the ACME system, the chief difference between regular tabletop play and abstract/mapless play.
DISTANCES
Distances on the notional "game board" are reduced to five basic levels. There are really seven, if you consider 0 (right on top of each other) and extreme far range (too far for magic missiles and long bows)... but the five listed below are the ones that will be dealt with the most often. These distances are all relative. A character can't simply be "adjacent" in general, but must be adjacent to someone. Both such adjacent characters might be near to a third, and the whole cluster of three characters might be at close range to a fourth.
Adjacent: The equivalent of right next to each other, one square over from each other.
Near: The equivalent of two squares over... i.e., with one square in between. All creatures who are either near or adjacent to you are "nearby".
Close Range: Roughly within five squares of each other. Anything in Close Range or nearer is "close by".
Far Range: Roughly within ten squares of each other. Combat usually starts with combatants this distance apart or closer.
Very Far Range: Roughly within twenty squares of each other.
CLUSTERS
A cluster refers to a group of characters that are bunched up around each other. At the start of an encounter, the PCs are usually in a cluster, unless they're deliberately spread out or have had time to move into specific positions on the field. They can decide if they're adjacent or near to each other. Their opponents will often be arranged in more than one cluster.
Clusters are not rigid and absolute divisions of characters. Members of a cluster may all be nearby each other (a dense cluster may have members that are standing adjacent), but a "cluster" is not a set unit of distance/width. Clusters are a tool for the DM to use in laying out the battlefield with some sense of space, as they allow enemies to be grouped closer to or farther from the PCs, or positioned at strategic or interesting points in the room. For PCs they provide tempting targets for burst and blast attacks and ways of engaging with smaller numbers of enemies at a time.
MOVING
If you're moving towards or away another character, then your movement speed is compared very roughly to the distance to determine how many move actions it will take (usually two to move from far range to adjacent, usually one to move from close range to adjacent or far range).
Tactics such as using a move action to move half the distance and then a standard action to charge the rest of it are still valid in the ACME system. Running, with its attendant bonuses and penalties, is the same as well. If it's important, exact movement speeds may be used to adjudicate tricky situations, i.e., if an enemy you just moved away from can catch up to you without running or charging.
If you don't want to approach an enemy head-on, to avoid dangerous terrain or traps, you can specify that you're "going around". This will eat up your movement at a rate determined by the DM. Feel free to discuss exactly what you're doing beforehand. Characters with higher than normal Move scores can expect a little more leeway, in relation to characters with lower Move scores.
FLANKING
Since the ACME system does not keep track of exact absolute positions, flanking can only be done intentionally, not simply by occupying space. You must shift into position while adjacent to an enemy to form a flank.
If you and an ally are both adjacent to the same enemy, you can spend a move action to shift and flank the enemy. This leads to both you and your ally having Combat Advantage against the enemy, as normal. Again, just moving adjacent to an enemy is not enough to form a flank. You must be able to shift after you're already adjacent, whether as part of another move action or as part of an action that lets you shift multiple times.
You cannot flank (or be used by an ally to form a flank) if you are flanked yourself. You must move to break the flank before you can shift to form a new one. You cannot be flanking multiple enemies at the same time.
BOXED IN
The boxed in condition represents the possibility of being truly surrounded, something that's easy to work out with a board and miniatures but somewhat harder to adjudicate in the abstract.
If more than one pair of enemies is flanking you, you are boxed in. While you are boxed in, you cannot move unless you teleport, fly, or use an ability that lets you move through an enemy's space or switch spaces with an enemy. You can also free yourself or be freed by ally, if you are able to shift or be slid x number of squares at once, with x being equal to the number of times you're flanked.
That is, if two pairs of enemies are flanking you, you need to be able to shift 2 squares or be slid 2 squares by an ally. This gets you free of all the flanks, though you're still adjacent to the enemies.
Alternatives to escaping from being boxed in may include situational uses of skills like Athletics or Acrobatics, or ending one of the flanks by defeating an enemy or pushing them away.
Creatures who are larger than Medium sized may require more flankers to be boxed in, at the DM's discretion.
DIFFICULT TERRAIN
The idea of difficult terrain works more or less as normal. Its position will usually be in relation to a cluster of NPCs: in front of them, or all around them.
If difficult terrain is between the PCs and a cluster of enemies, the DM should have an idea how much more movement it costs to go through it, or around. For encounter design purposes, it should usually take longer to go around, since the consequences of being caught on it (cannot shift) are worth avoiding.
FLIGHT
Flight functions as normal. The abstract distances may be vertical as well as horizontal. A character who is flying can usually bypass difficult terrain and non-flying guards.
TELEPORTATION
Teleportation works like normal movement in terms of getting closer or farther away from other characters. However, it lets you avoid Opportunity Attacks, bypass difficult terrain, and slip out of flanks without shifting. If you teleport adjacent to an enemy who is adjacent to an ally, you can create a flank (if such is otherwise possible) without shifting.
FORCED MOVEMENT
If you have a power that lets you push, pull, or slide another character, it's treated as normal movement. A push must move the target away from you and a pull must move them closer, as normal. A slide can do either. If you wish to do anything more fancy or elaborate, like knock an enemy off a cliff or into a fire, or slide an ally into a flanking position, or slide an enemy in between two allies to create a flank, you must make a check using the same attribute as the attack (or your class's primary attribute, if the power doesn't have one) with a bonus equal to the amount of forced movement to see if you can pull it off.
The DC is set by the DM, though it will usually be the Reflexes of the target if what you're trying to do is not conducive to the target's health. The DM is free to say that what you're trying is not possible. In general a slide will afford more freedom to be creative than a push or pull.
GUARDING
Guarding is a new mechanic for the ACME system, intended to represent the way a character can be positioned to block easy access to others. You can declare you are guarding one or two nearby allies by spending a move action, to represent getting into position. You remain guarding them as long as you are able to attack and until they are no longer nearby. While you are guarding, you grant them partial cover and anyone who comes directly towards them will pass by you, provoking an opportunity attack. You can also ready an action to attack the first enemy that approaches you.
Enemies can try to bypass your guard by using a move action to go around you. If they do not reach your allies on their turn, you can guard again on yours... using a new action to interpose yourself between the enemy and your allies once again. If enemies are approaching from more than one direction, you have to choose which approach to guard.
You cannot guard more than two allies at a time. You cannot guard an ally if you are being guarded... doing so ends the guard on you. Guarding requires your attention to be focused on your allies, so you cannot form a flank while guarding, and cannot guard while being flanked.
With the DM's permission, you can guard other things besides allies: a terrain feature or item, an enemy you don't want other enemies to reach, etc. No matter what you're guarding, you don't provide cover for anyone you don't want to.
ATTACKS
WHO CAN I TARGET?
Melee and Ranged attacks function more or less as normal. A melee attack with a range of 1 can only target adjacent creatures. If you have a "reach" attack or an attack with a range of 2, you can target nearby creatures. A range of 10 is sufficient to target any creatures out to far range, and 5 can target any creature out to close range. For other values, DM's discretion applies. With a shorter range (like 3), it may be necessary to spend a move action stepping closer without actually coming near to the target.
If your power targets one, two, or three creatures (whether enemies or allies) within a close burst, or targets all allies within a close burst, then it's resolved similarly: a burst 5 is sufficient to target anyone within Close Range, while a burst 10 can reach anyone out to Far Range. These powers often function more like Ranged attacks except for not provoking Opportunity Attacks
With Area, Bursts, and Blasts, things get more complicated. These attacks all target multiple squares on the battle mat, and often have the possibility of catching multiple enemies clustered together... or an ally who's too close.
CLOSE AND AREA BURST ATTACKS
If you have an attack that says "Close Burst x" or "Area Burst x in y squares" for the range, that burst includes all creatures who are adjacent to the origin of the attack (you, or the target within the indicated range if it's an area burst) if x is at least 1. If it's at least 2, then it targets all creatures who are nearby. And of course, the target of an Area attack is inside the burst.
After that, it's less certain.
Anybody who might possibly be within the burst and is a valid target of the attack is "threatened" by it. The DM rolls a d6 for each threatened creature. If the number is less than or equal to the size of the burst (x), then that creature is within the burst. For smaller bursts, this chance applies if a creature is clustered up around the origin. If the threatened creature is a minion, treat the burst size as 1 larger for resolving the threat.
Generally, creatures are threatened by a burst if they're in a cluster with the burst's target/origin. Depending on the size of the burst and exact situation, it's possible that others might be threatened. You can ask the DM who would be threatened before committing to the attack - in the real life being modeled by the game, you could at least eyeball it.
With Area Bursts, it's possible to target empty space in order to get clever and hit more enemies without hitting your allies. For instance, if two enemies are near to each other and you make one enemy the center of an Area Burst 1, you know you've missed the other and you need a threat roll for each of the others in the cluster. But by dropping an Area Burst 1 "in between" the two enemies, you know they're both effectively adjacent to the attack. That's two enemies who are definitely in the burst. This is a perfectly valid tactic when playing with a battle mat, and it remains viable in the ACME system.
Determining that a creature is in the burst only means that they're targeted by the attack. A hit roll is still needed to determine if they're affected. The rolling mechanic could slow down the game, which is why one person--the DM--rolls for everyone, in order to keep things moving.
In short: using bursts are good when enemies are in a cluster. If allies are fighting up close with those enemies, they may be caught in it.
Example #1: Scorching Burst is a Wizard spell that does an Area Burst 1 within 10 squares. The Wizard can cast it on any creature within Far Range. Any creatures known to be adjacent to the target are also caught within the burst, including the Wizard's own allies if they're engaged with it. If other enemies are in a cluster with the target, they might be caught in the burst, though there's only a 1 in 6 chance. This same possibility should be rolled for any allies who are adjacent to these enemies... they are in the cluster, too.
Example #2: A Kobold Dragonshield is guarding a Wyrmpriest. The Wizard decides to drop a Scorching Burst right between them. The two are both automatically caught in the burst. Any other kobolds who are in the same cluster might be caught in the burst... the DM rolls 1d6 for each of them.
CLOSE BLASTS
If you have an attack that says "Close Blast x" (usually 3 or 5), it's resolved a little differently. The ACME system makes use of a new mechanic, not present in the normal game. This is Wide Blasts and Narrow Blasts. You can choose to use either a Wide Blast or a Narrow Blast when you use the power. If you use a Narrow Blast, then you can target a number of nearby creatures equal to x. For instance, a Close Blast 3 power can target up to 3 nearby creatures with a Narrow Blast.
If that's not enough, you can use a Wide Blast. The Wide Blast lets you pick the same number of targets. Anyone else who is nearby or might possibly be caught in the blast is threatened by it. The threat is resolved exactly the same as for a burst, including the +1 chance for minions.
Flanking Limitation: Blasts are directional. You can't use them to scatter two opponents on opposite sides of you. Therefore, out of each pair of enemies that are flanking you, one member of the pair must be exempted from the blast. They can't be picked as targets. They cannot be randomly affected by a Wide Blast.
Example #1: A Wizard is being guarded by an ally, a Warden. A horde of minions threatens to overrun the pair. The Wizard uses Thunderwave, which does a Close Blast 3 attack. Not wishing to endanger the Warden, the Wizard makes it a Narrow Blast and targets only the three minions that are directly attacking the Wizard. The other minions aren't threatened, but neither is the Warden.
Example #2: A Ranger who is a Half-Elf is off alone, sniping enemies with a bow. A horde of minions break away and surround the Ranger. The Ranger uses Thunderwave as a Half-Elf Dilettante power. With no allies nearby, the Ranger uses a Wide Blast. Three of the minions are automatically included in the blast. The others are threatened, and will be affected on a roll of 4 (3 + 1) or lower on a d6.
The Wide/Narrow blast choice differs from ordinary play, but the effect is similar: when you have a board with an exact known position for allies and enemies, you can usually use a blast power conservatively to hit a small number of opponents and miss your allies, if you choose.
OPPORTUNITY ATTACKS
Opportunity Attacks are provoked by the same things as normal: if an enemy is adjacent to you and moves without shifting, or uses a ranged or area burst attack. If it seems like an enemy would reasonably be moving past your character (because it's fleeing and you're positioned inside a bottleneck, or you're hiding near its likely path), the DM may grant you an Opportunity Attack. If it seems really likely that an enemy would be passing by you, feel free to ask... but doing so every time an enemy moves on the off-chance that they're wandering close to you may be hazardous to character health.
Some Explanations, or What I Was Thinking:
It would be the DM's job to keep track of where everyone is and give an overview of the combat field every round. This should ideally be presented in a visual form that players can refer back to, rather than having to keep the whole battlefield in their head. My thought is that for an online game, I would describe the battlefield positions in a block of text and for an offline game I would list the clusters on a white board or a sheet of paper.
The change to flanking (that you can't flank while being flanked) is to keep the number of flanks going on at one time, since each one is something that has to be kept track of (unlike in a tabletop game, when you glance at the board and see that your opponent is flanked.) The flanking rules and boxing in rules together are designed to create a sense of a dynamic combat with warriors jockeying for position, as tends to happen in 4E tabletop games. They also give more meaningfulness to the "shift" mechanic, since so many powers allow free shifts.
Guarding is meant to allow Defenders to do their job without the game devolving to something even worse than "I shot you!"/"No, you didn't, you missed!" -- "I stood in your way!"/"No, you didn't!"