Mission 15 - Guardians
Difficulty: Heroic (May unlock on Easy)
Once you reach the energy cores, clear out the enemies, and work your way up to the left side to find another energy core at the top of the hill. Once ready, climb the tall rock nearby and ground the energy core (jump and hold melee). It should be destroyed with a single hit if done correctly.
Coordinate your ground pound with a friend at another core to unlock this as well: