Eternal Guardian is a skill located in the Animal Companions (which can be found in the Warden skill tree). Eternal Guardian is an ultimate. Eternal Guardian is a morph of Feral Guardian.
Eternal 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.