Vengeful Surge — The death of a companion awakens a surge of energy, increasing damage dealt by 100% and attack speed by 50%.
Tactics
Casts orbs which buff its twin. Buff gives +60% damage and an aoe ability.
If its twin dies, gains +100% damage, +50% haste
Line of sight does not affect the orb.
Keep them somewhat apart from each other, but not so far that they gain the "separation anxiety" buff (+150% dmg).
When the orb spawns, kill it fast to avoid the +60% buff from occurring. The center of the two circles is an excellent place to position them.
They both need to die at about the same time.
Occasionally an orb may travel to a mob that has not been pulled. This mob will gain the buff but will NOT aggro the raid unless provoked.