Your spirit companion channels the spirit of an ancestral warrior, which helps your spirit companion cover your allies' retreat.

Encounter   ✦     Implement, Primal, Spirit
Standard Action      Melee spirit 1

Target: One creature

Attack: Wisdom vs. Fortitude

Hit: 2d8 + Wisdom modifier damage. Until the end of your next turn, you and your allies gain a +5 bonus to all defenses against opportunity attacks while adjacent to your spirit companion.

Published in Player's Handbook 2, page(s) 122.