The Orb of Destruction, though it costs a whopping 3 black/3 normal energy, can destroy anything for the same cost. It deals 2 damage to you, but can get rid of anything you want--like an Orb of Unity, a powerful Soulseeker, etc. The cost and recoil are damaging, but worth it in the right situation. Be careful not to kill yourself accidentally, though!
Strong against: strong things, annoying things, other peoples' strategies.
Weak against: object removal, having low HP (best to place this in a healing deck with cards like Vampiric Bite to have those extra HP to spare).