Swarm, Abyssal Ant (CR 16)

Medium Aberration (Extraplanar and Swarm-Diminutive)
Alignment: Always chaotic evil
Initiative: +5 (+1 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., Listen +15, and Spot +13
Languages: understand Abyssal, do not speak

AC: 17 (+1 Dex, +6 natural), touch 11, flat-footed 16
Hit Dice: 20d8+60 (150 hp)
Fort +11, Ref +9, Will +15
Speed: 40 ft., climb 20 ft.
Space: 10 ft./0 ft.
Base Attack +15; Grapple -
Attack: Swarm, or spit acid +16 ranged touch
Full Attack: Swarm
Damage: Swarm 4d6 plus 2d8 acid, spit acid 2d8
Special Attacks/Actions: Acid, distraction (DC 23), penetration
Abilities: Str 1, Dex 12, Con 16, Int 7, Wis 12, Cha 13
Special Qualities: Acid immunity, cold resistance 10, electricity resistance 10, fire resistance 10, hive mind, poison immunity, SR 22, swarm traits
Feats: Alertness; Great Fortitude; Improved Initiative; Iron Will; Lightning Reflexes; Point Blank Shot; Skill Focus (Climb)
Skills: Climb +14, Listen +15, and Spot +13
Advancement: -
Climate/Terrain: Any land and underground (Abyss)
Organization: Solitary or army (3-8 swarms)
Treasure/Possessions: -

Source: Fiend Folio

Like plague ants, abyssal ants exhibit little interest in tactics. As a swarm, they do possess a modicum of intelligence and have been known to retreat from unsuccessful attacks.

Acid (Ex): The swarm attack of an abyssal ant swarm deals acid damage in addition to the normal damage of the creatures' bites and stings. Also, a swarm of abyssal ants can produce a shower of acidic spittle that works as a grenadelike weapon, dealing 2d5 points of damage on a direct hit and 1d4 points of splash damage to creatures within 5 feet of the target. Creatures directly hit by the acid take an additional 1d8 points of damage 1 round after being hit.

Penetration (Su): The swarm attack of an abyssal ant swarm penetrates damage reduction as if it were a +5 weapon.

Hive Mind (Ex): An abyssal ant swarm has a hive mind, which makes it susceptible to mind-affecting spells. For purposes of such spells, the swarm is a single creature of the aberration type.

Skills: Abyssal ant swarms have a +8 racial bonus on Climb checks and can always choose to take 10 on Climb checks, even if rushed or threatened.

Distraction (Ex): Any non-mindless creature vulnerable to a swarm's 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) negates the effect. Spellcasting or concentrating on spells within the area of a swarm requires a Concentration check (DC 20 + spell level). Using skills requiring patience and concentration requires a Concentration check )DC 20).

Swarm 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 fewer causes the swarm 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 another.

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 effects if the swarm has an Intelligence score and a hive mind. A swarm takes a -10 penalty on saving throws against spells or effects that affect an area, such as many evocation spells or grenadelike weapons. If the area attack does not allow a saving throw, a swarm takes double damage instead,

Swarms made up of Diminutive or Fine creatures are susceptible to high winds such as that created by a gust of wind spell. To determine the effect of wind on a swarm, treat the swarm as a creature of the same size as its constituent creatures. For example, a swarm of Abyss ants (Diminutive creatures) can be blown away by a severe wind. Wind effects deal 1d6 points of subdual damage to the swarm per spell level or Hit Die of the originating creature, in the case of effects such as an air elemental's whirlwind). A swarm that takes subdual damage sufficient to exceed its current hit points becomes disorganized and dispersed, and does not re-form until its current hit points exceed its subdual damage.

Extraplanar Subtype

A subtype applied to any creature when it is on a plane other than its native plane. A creature that travels the planes can gain or lose this subtype as it goes from plane to plane. This book assumes that encounters with creatures take place on the Material Plane, and every creature whose native plane is not the Material Plane has the extraplanar subtype (but would not have when on its home plane). An extraplanar creatures usually has a home plane mentioned in its description. These home planes are taken from the Great Wheel cosmology of the D&D game (see Chapter 5 of the Dungeon Master's Guide). If your campaign uses a different cosmology, you will need to assign different home planes to extraplanar creatures.

Creatures not labeled as extraplanar are natives of the Material Plane, and they gain the extraplanar subtype if they leave the Material Plane. No creature has the extraplanar subtype when it is on a transitive plane; the transitive planes in the D&D cosmology are the Astral Plane, the Ethereal Plane, and the Plane of Shadow.