Ixitxachitl, Vampiric (CR 3)

Small Aberration (Aquatic)
Alignment: Always chaotic evil
Initiative: +3 (Dex); Senses: darkvision 60 ft., Listen +4, and Spot +4

AC: 16 (+1 size, +3 Dex, +2 natural), touch 14, flat-footed 13
Hit Dice: 2d8+2 (11 hp)
Fort +1, Ref +3, Will +4
Speed: Swim 30 ft.
Space: 5 ft./5 ft.
Base Attack +1; Grapple -2
Attack: Bite +3 melee
Full Attack: Bite +3 melee
Damage: Bite 1d6+1 plus energy drain
Special Attacks/Actions: Energy drain
Abilities: Str 12, Dex 16, Con 13, Int 12, Wis 13, Cha 7
Special Qualities: fast healing 5
Feats: Dodge
Skills: Hide +10, Knowledge (nature) +4, Listen +4, Spot +4, Swim +9, and Tumble +6
Advancement: 3-4 HD (Small); 5-6 HD (Medium-size); 7-8 HD (Large); or by character
Climate/Terrain: Warm aquatic
Organization: Solitary, pair, pod (1-2 plus 5-12 average ixitxachitls and 1 2nd-level cleric), or shoal (1-2 plus 10-100 average ixitxachitl, 5 2nd-level clerics, 2 5th-level clerics, and 20-200 slaves)
Treasure/Possessions: No coins, no goods, double items (no weapons, potions, or scrolls)

Source: Monster Manual II

Energy Drain (Su): Any living creature hit by a vampiric ixitxachitl's bite attack gains one negative level. For each negative level bestowed, the vampiric ixitxachitl heals 5 points of damage. If the amount of healing is more than the damage the creature has taken, it gains any excess as temporary hit points. If the negative level has not been removed (with a spell such as restoration) before 24 hours have passed, the afflicted opponent must succeed at a Fortitude save (DC 12) to remove it. (The vampiric ixitxachitl uses its Constitution modifier instead of its Charisma modifier to determine the save DC.) Failure means the opponent's level (or Hit Dice) is reduced by one.

Fast Healing (Ex): A vampiric ixitxachitl regains lost hit points at the rate of 5 per round. Fast healing does not restore hit points lost from starvation, thirst, or suffocation, and it does not allow the vampiric ixitxachitl to regrow or reattach lost body parts.

Vampiric ixitxachitls prefer to hang back, hidden, and allow their underlings to enter combat while they size up the opposition. If the fight is going well, they join in, looking for easy targets. If the outcome seems doubtful, they try to support their underlings in strikes against the most dangerous-looking foe.

Aquatic Subtype

Creatures with the aquatic subtype always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.