Quasit

From Dungeons & Dragons Monster Manual (2014):

Quasits infest the Lower Planes. Physically weak, they keep to the shadows to plot mischief and wickedness. More powerful demons use quasits as spies and messengers when they aren’t devouring them or pulling them apart to pass the time.

A quasit can assume animal forms, but in its true form it looks like a 2-foot-tall green humanoid with a barbed tail and horns. The quasit has clawed fingers and toes, and these claws can deliver an irritating poison. It prefers to be invisible when it attacks.

Mortal spellcasters interested in extraplanar familiars find quasits easy to summon and eager to serve. The quasit plays the part of the obsequious servant. It serves its master well, but it goads the mortal to greater and greater acts of chaos and evil.

From Planescape Monstrous Compendium Appendix I (1994):

Quasits are chaotic evil counterparts to imps. The chaotic evil priests and wizards which quasits “serve” gain the same benefits and disadvantages that an imp’s master does. Like imps, each quasit can assume two other forms. Those most commonly chosen by quasits are bats, giant centipedes, frogs, or wolves. They can use their magic in any of their forms.

The quasit attacks with its clawed hands (doing 1-2 points each) and its deadly bite (doing 1-4 points). The quasit’s claws are coated in a toxin which causes anyone struck by them to save versus poison or lose one point of dexterity for 2-12 (2d6) rounds. The effects of multiple wounds are cumulative.

Quasits can turn invisible, detect good, or detect magic at will. They regenerate 1 hit point per round and can unleash a blast of fear with a 30 foot range radius once per day. Once each week the quasit can commune with the lower planes (asking up to 6 questions).

Quasits can only be harmed by cold iron or magical weapons. They are able to resist magic 25% of the time, save as if they were 7 Hit Die monsters and are immune to cold, fire, and lightning.