Diminutive, dark, bat-winged humanoid with a poisonous tail stinger

An Imp is a diminutive, dark, bat-winged humanoid standing about 2 feet tall with a dagger-like tail stinger. It is able to change at-will into the form of a massive spider, raven, or giant rat, all with a devilish look. In all forms the imp has Darkvision with a range of 60 feet. In its natural form, an imp attacks with its poisonous stinger; those struck must save vs. Poison or die suffering tremendous pain. In its other forms it cannot use its poison attack.

Small devil formed from soul worms, serving evil priests or sorcerers as familiars

Imps are formed from soul worms, created by archdevils to spread evil through service to a lawful evil priest or sorcerer. They are very rarely encountered on the Prime Material Plane, but are commonly seen in the lower planes. They have only average intelligence, but in their role as familiars they are able to rely on the knowledge of their archdevil master. Imps are created with the innate ability to polymorph self. The GM should choose two of the following forms (giant rat, goat, large spider, raven). In their polymorphed form, imps are limited to that animal's natural attacks. In their natural form, imps attack with their poison-tipped tail stingers. Any victim struck must save vs poison or die. When serving as a familiar to an evil magic user or cleric, the Imp imparts the following benefits to its master: Constant full-sensory telepathic contact between the Imp and the master up to 1 mile in range. If the master is within 25-ft of the imp, the former gains the Imp's 25% magic resistance and its regeneration ability (1 hp/round). If the master is within 1 mile of the Imp, the former gains an additional level of ability. However, if the imp is killed, the master immediately l