Feral Guardian is a skill located in the Animal Companions (which can be found in the Warden skill tree). Feral Guardian is an ultimate. Feral Guardian is a base skill, and can be morphed into Eternal Guardian or Wild Guardian.
Feral Guardian 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, Master at Arms, Spell Erosion. Also the following red champion point trees protect against this skill: Elemental Defender, Iron Clad.