Not at the beginning of their turn: Swarm Attacks

Update: The world has been saved! Needlefang Drake Swarms were toned down to a manageable level in the Great November Errata. Also, swarms from later books such as Monster Manual 2 feature much more reasonable auras, so the problem I talked about only affects a couple of monsters in the first MM now.

Swarms. Deadly, disgusting swarms. These little guys feature some of the most inspired game mechanics in Monster Manual. Their rules include a generous bunch of resistances, vulnerabilities and special abilities, all dripping with flavor. Amazingly, their complexity level has been kept at bay, so using these monsters in an encounter won't result in a noticeable slowdown in gameplay. I think they can even make a great contribution to game strategy and role balance, as they make increase so much the value of area attacks - the perceived utility of controller PCs would improve a lot if swarms were a more common monster choice for encounters.

For all their good features, swarms have one fatal flaw that is probably preventing them to see as much play as they deserve. Even if I'd like every other encounter to include a swarm of two, this is currently not a realistic, nor a recommended option. Unlike most monsters, you just can't expect to replace a couple of guys in an encounter with swarms of the same level without drastically changing the difficulty - swarms are very powerful, their value often closer to an Elite monster than to a standard one. Clearly, this has to be addressed.

Even though they have great defenses (making them the bane of any party lacking good area powers), what really breaks swarms, in my opinion, is their unmatched offensive capability. Consider this:

Swarm Attack - aura 1; the swarm makes a basic attack as a free action against each enemy that begins its turn in the aura.

Assuming its basic attacks deal average damage (and they almost always do), every swarm has a good, built-in area attack. This would actually be an acceptable deal if it was their main attack, but unfortunately, it's not. Swarms can actually use this aura in addition to a Standard Action attack (usually the same basic attack), so they get to attack an enemy of their choice twice per round. Normally, this amounts to double the damage that another monster of the same level would deal against a single target, on top of standard damage against the rest of enemies within the area. Total Party Kill is a frequent outcome.

The solution

Something needs to get changed. Although there are many possible fixes, the one I like the most is the one I applied to warrior stances in this article: change the aura effect to trigger at the end of each enemy's turn. This would be my revision:

Swarm Attack - aura 1; the swarm makes a basic attack as a free action against each enemy that ends its turn in the aura.

Having the damage happen at the end of turn instead of inconditionally makes swarms more interactive, as well as weaker. It even makes sense from a flavor perspective, as it means that PCs will actively run away from swarms, and they will rarely charge against them. However, players will soon learn that these new swarms are anything but tame, when they have to figure out how to escape (without provoking OAs) the damaging aura of a monster that can enter their space and is immune to forced movement. Excuse me for a moment while I cackle maniacally.

Bonus monster: Fixed Needlefang Drake Swarm.

My suggested change should be enough to neuter most swarms, but there are a few that would remain troublesome even after this. Needlefang Drake Swarms are probably the most overpowered monsters in the MM, featuring unbearably high damage even without their swarm aura, as well as their sick, spammable Pull Down attack.

The following version has that damage significantly reduced, and further restricts the use of Pull Down. Still, five of these should prove a terrifying vision for even the strongest adventuring parties: