Corpse Ratswarm (CR 4)
AC: 13 (+2 size, +1 Dex), touch 13, flat-footed 12
Hit Dice: 8d12 (52 hp); DR: 5/slashing
Fort +2, Ref +3, Will +6
Speed: 15 ft., climb 15 ft.
Space: 10 ft./0 ft.
Base Attack +4; Grapple -
Full Attack: Swarm
Damage: Swarm 1d6 plus disease
Special Attacks/Actions: Disease, distraction
Abilities: Str 4, Dex 13, Con -, Int -, Wis 10, Cha 1
Special Qualities: swarm traits, undead traits
Organization: Solitary, pack (2-4 swarms), or infestation (7-12 swarms)
Disease (Ex): Filth fever-swarm attack, Fortitude DC 16, incubation period 1d3 days, damage 1d3 Dex and 1d3 Con. The save DC is Constitution-based and includes a +2 racial bonus.
Distraction (Ex): Any living creature that begins its turn with a corpse tar swarm in its space must succeed on a DC 15 Fortitude save or be nauseated for 1 round The save DC is Constitution-based
A corpse rat swarm seeks to engulf and devour any living prey it encounters. A corpse rat swarm deals 1d6 points of damage so any creature whose space it occupies at the end of its move.
Like a bone rat swarm, a corpse rat swarm is made up of countless undead rats. These, however, are closer to zombies than skeletons, with hunks of rotting flesh still hanging on their bones. They are even more disease-ridden than a normal rat swarm, and every bit as hungry for flesh.
A swarm is a collection of Fine, Diminutive, or Tiny creatures that acts as a single creature. A swarm has the characteristics of its type, except as noted here. A swarm has a single pool of Hit Dice and hit points, a single initiative modifier, a single speed, and a single Armor Class. A swarm makes saving throws as a single creature.
A single swarm occupies a square (if it is made up of nonflying creatures) or a cube (of flying creatures) 10 feet on a side, but its reach is 0 feet, like its component creatures. In order to attack, it moves into an opponent's space, which provokes attacks of opportunity. It can occupy the same space as a creature of any size, since it crawls all over its prey. A swarm can move through squares occupied by enemies and vice versa without impediment, although the swarm provokes attacks of opportunity if it does so. A swarm can move through cracks or holes large enough for its component creatures.
A swarm of Tiny creatures consists of 300 nonflying creatures or 1,000 flying creatures. A swarm of Diminutive creatures consists of 1,500 nonflying creatures or 5,000 flying creatures. A swarm of Fine creatures consists of 10,000 creatures, whether they are flying or not. Swarms of nonflying creatures include many more creatures than could normally fit in a 10-foot square based on their normal space, because creatures in a swarm are packed tightly together and generally crawl over each other and their prey when moving or attacking. Larger swarms are represented by multiples of single swarms. (A swarm of 15,000 centipedes is ten centipede swarms, each swarm occupying a 10-foot square.) The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares.
Traits: A swarm has no clear front or back and no discernible anatomy, so it is not subject to critical hits or flanking. A swarm made up of Tiny creatures takes half damage from slashing and piercing weapons. A swarm composed of Fine or Diminutive creatures is immune to all weapon damage.
Reducing a swarm to 0 hit points or lower causes it to break up, though damage taken until that point does not degrade its ability to attack or resist attack. Swarms are never staggered or reduced to a dying state by damage. Also, they cannot be tripped, grappled, or bull rushed, and they cannot grapple an opponent.
A swarm is immune to any spell or effect that targets a specific number of creatures (including single-target spells such as disintegrate), with the exception of mind-affecting spells and abilities (charms, compulsions, phantasms, patterns, and morale effects) if the swarm has an Intelligence score and a hive mind. A swarm takes half again as much damage (+50%) from spells or effects that affect an area, such as splash weapons and many evocation spells.
Swarms made up of Diminutive or Fine creatures are susceptible to high winds such as that created by a gust of wind spell. For purposes of determining the effects of wind on a swarm, treat the swarm as a creature of the same size as its constituent creatures (see Winds, page 95 of the Dungeon Master's Guide). For example, a swarm of locusts (a swarm of Diminutive creatures) can be blown away by a severe wind. Wind effects deal 1d6 points of nonlethal damage to a swarm per spell level (or Hit Dice of the originating creature, in the case of effects such as an air elemental's whirlwind). A swarm rendered unconscious by means of nonlethal damage becomes disorganized and dispersed, and does not re-form until its hit points exceed its nonlethal damage.
Swarm Attack: Creatures with the swarm subtype don't make standard melee attacks. Instead, they deal automatic damage to any creature whose space they occupy at the end of their move, with no attack roll needed. Swarm attacks are not subject to a miss chance for concealment or cover. A swarm's statistics block has "swarm" in the Attack and Full Attack entries, with no attack bonus given. The amount of damage a swarm deals is based on its Hit Dice, as shown below.
|Swarm HD||Swarm Base Damage|
|21 or more||5d6|
A swarm's attacks are nonmagical, unless the swarm's description states otherwise. Damage reduction sufficient to reduce a swarm attack's damage to 0, being incorporeal, and other special abilities usually give a creature immunity (or at least resistance) to damage from a swarm. Some swarms also have acid, poison, blood drain, or other special attacks in addition to normal damage.
Swarms do not threaten creatures in their square, and do not make attacks of opportunity with their swarm attack. However, they distract foes whose squares they occupy, as described below.
Distraction (Ex): Any living creature vulnerable to a swarms damage that begins its turn with a swarm in its square is nauseated for 1 round; a Fortitude save (DC 10 + 1/2 swarm's HD + swarm's Con modifier; the exact DC is given in a swarm's description) negates the effect. Spellcasting or concentrating on spells within the area of a swarm requires a Concentration check (DC 20 + spell level). Using skills that involve patience and concentration requires a DC 20 Concentration check.