Imps are descendants of outsiders from the plane of Hell that became native to the material plane after extended exposure.
Stinger
Imps can attack with a special unarmed strike, in the form of their stinger, that deals lethal damage, doesn't count as archaic, and threatens squares.
Additionally, an imp can load their stinger with venom as part of their attack action. Once loaded, a creature that takes at 1 point of damage from the stinger is poisoned and the stinger is no longer loaded. Once an imp loads their sting it remains loaded until they successfully deal damage to an opponent. They cannot load their sting again until they've spent a Resolve Point to recover Stamina Points after a 10-minute rest. They also cannot load their sting if it is already loaded.
Imp Venom; Type poison (injury); Save Fortitude DC 10 + the imp's level + their Constitution modifier; Track Dexterity; Frequency 1/round for 6 rounds; End State Immobile
Imps gain a special version of the Weapon Specialization feat with their sting at 3rd level, allowing them to add 1–1/2 × their character level to their damage rolls for this unarmed strike (instead of just adding their character level, as usual).