Questions about swarms.

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So in my last session as DM I had 2 Angry Mobs (from the monster builder) of sick villagers going insane. They were in quarantine, walled off (with bars like a giant jail cell) and banging at the door to get out. Not to go into details but a priest managed to get over the wall and was attacked by the mobs. The party wanted to help. So they formed a plan to open the door, slide the priest through and close the door immediately after. I was forced to tell them that a swarm is considered difficult terrain therefor they couldn't slide through the swarm that was blocking the door. Was that correct? Also was there any way for them to have saved him using controlling powers? They had no access to teleport.

In case you're wondering about the conclusion: The tank ended up entering the quarantine with the door shut behind him. Got knocked prone a couple of times by the mob but eventually picked up the priest and got out.

So after this session I realized that I don't quite understand swarm rules and have a couple of questions. I've copy pasted the compendium entry on swarms bellow:

A swarm is composed of multiple creatures but functions as a single creature. A swarm can occupy the same space as another creature, and an enemy can enter a swarm’s space, which is difficult terrain. A swarm cannot be pulled, pushed, or slid by melee or ranged attacks.
    A swarm can squeeze through any opening large enough for even one of its constituent creatures. For example, a swarm of bats can squeeze through an opening large enough for one of the bats to squeeze through.

  1. Can a swarm occupy the same space as another swarm? Would their movement be subject to difficult terrain even if the swarm occupies only one square of the other swarm?

  2. "A swarm cannot be pulled, pushed, or slid by melee or ranged attacks." Does this mean that they can be forced to move by area attacks?

Johnstan wrote:

So in my last session as DM I had 2 Angry Mobs (from the monster builder) of sick villagers going insane. They were in quarantine, walled off (with bars like a giant jail cell) and banging at the door to get out. Not to go into details but a priest managed to get over the wall and was attacked by the mobs. The party wanted to help. So they formed a plan to open the door, slide the priest through and close the door immediately after. I was forced to tell them that a swarm is considered difficult terrain therefor they couldn't slide through the swarm that was blocking the door. Was that correct? Also was there any way for them to have saved him using controlling powers? They had no access to teleport.

  They could have used any sort of forced movement on the priest to get him out (at least if the Angry Mobs were the only obsocle).  All modes of forced movement ignore difficult terrain (see Rules Compendium page 212)

Johnstan wrote:

In case you're wondering about the conclusion: The tank ended up entering the quarantine with the door shut behind him. Got knocked prone a couple of times by the mob but eventually picked up the priest and got out.

So after this session I realized that I don't quite understand swarm rules and have a couple of questions. I've copy pasted the compendium entry on swarms bellow:

A swarm is composed of multiple creatures but functions as a single creature. A swarm can occupy the same space as another creature, and an enemy can enter a swarm’s space, which is difficult terrain. A swarm cannot be pulled, pushed, or slid by melee or ranged attacks.
    A swarm can squeeze through any opening large enough for even one of its constituent creatures. For example, a swarm of bats can squeeze through an opening large enough for one of the bats to squeeze through.

  1. Can a swarm occupy the same space as another swarm? Would their movement be subject to difficult terrain even if the swarm occupies only one square of the other swarm?

  2. "A swarm cannot be pulled, pushed, or slid by melee or ranged attacks." Does this mean that they can be forced to move by area attacks?

1. From what I can find, yes, they can share the same space.  Note that difficult terrain costs extra movement when entering the square.  So when swarm A moves so that any of its spaces will overlap with swarm B, it has to spend the extra movement for the difficult terrain (1 square extra movement no matter how much is overlapping.

2. Yes, forced movement from Close Burst (ex: Visions of Avarice secondary attack), Close Blast (ex: Thunderwave) and Area Burst (ex: Mists of Disarray) powers all work on Swarms.  The point is that a melee or ranged attack with a push/pull/slide would only affect a single creature in the swarm, while a blast or burst fills the square and effects all creatures in the swarm in that square (which is also why swarms usually take extra damage due to vulneraiblity to close and area attacks.)

 

Ah I feel dumb. I thought because you can't shift into difficult terrain that that applied to forced movement as well. I will update my group. Thank you so much for the clarification I really appreciate it.

For the record: you can shift into difficult terrain.  You just have to be shifting more than one square at once in order to do so.  So, for most characters, taking the shift action won't get you into difficult terrain, but, for instance, using the Ranger 2nd level utility 'invigorating stride' and having a wis mod of 2 or more, might.

Harrying your Prey, the Easy Way: A Hunter's Handbook - the first of what will hopefully be many CharOp efforts on my part. The Blinker - teleport everywhere. An Eladrin Knight/Eldritch Knight. CB != rules source.
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