Unstable Familiar is a skill located in the Daedric Summoning (which can be found in the Sorcerer skill tree). Unstable Familiar is a base skill, and can be morphed into Unstable Clannfear or Volatile Familiar.
Unstable Familiar deals the following types of damage: Shock Damage. Which means that it gets buffed by the following blue champion point trees: Elemental Expert, Elf Born, Master at Arms, Spell Erosion. Also the following red champion point trees protect against this skill: Elemental Defender, Iron Clad.