Cripple is a skill located in the Siphoning (which can be found in the Nightblade skill tree). Cripple is a base skill, and can be morphed into Debilitate
or Crippling Grasp
Cripple deals the following types of damage: Magic Damage. Which means that it gets buffed by the following blue champion point trees: Elemental Expert, Elf Born, Spell Erosion, Thaumaturge. Also the following red champion point trees protect against this skill: Elemental Defender, Thick Skinned.