Swarm, Viper (CR 3)

Medium Animal (Swarm-Diminutive)
Alignment: Always neutral
Initiative: +2 (Dex); Senses: low-light vision, scent, Listen +7, and Spot +7

AC: 16 (+2 Dex, +4 natural), touch 12, flat-footed 14
Hit Dice: 5d8+5 (27 hp)
Fort +5, Ref +6, Will +2
Speed: 15 ft., climb 15 ft.
Space: 5 ft./0 ft.
Base Attack +3; Grapple -
Attack: Swarm
Full Attack: Swarm
Damage: Swarm 1d6 plus poison
Special Attacks/Actions: Distraction (DC 13), poison
Abilities: Str 1, Dex 15, Con 12, Int 1, Wis 12, Cha 2
Special Qualities: Hive mind, swarm traits
Feats: -
Skills: Balance +10, Climb +12, Hide +8, Listen +7, and Spot +7
Climate/Terrain: Warm land and underground
Organization: Swarm

Source: Fiend Folio

Poison (Ex): A viper swarm delivers its poison (Fort DC 13 negates) with each swarm attack. Initial and secondary damage are the same (1d4 Con).

Hive Mind (Ex): A viper swarm has a hive mind, making it susceptible to mind-affecting spells. For purposes of such spells, the swarm is a single creature of the animal type.

Scent (Ex): A viper swarm can detect approaching enemies, sniff out hidden foes, and track by sense of smell.

Skills: Viper swarms have a +4 racial bonus on Hide, Listen, and Spot checks, and a +8 racial bonus on Balance checks. They use their Dexterity modifier for Climb checks and 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).

A single Diminutive viper's poison is painful but not deadly; several doses of it, however, can bring down an elephant. Viper swarms overwhelm their prey with poison, then feast on its still-warm flesh.

A viper swarm can be summoned using a summon nature's ally VI spell.