Soulgorger Orgg
A 6/6 trampler for five mana is a clean rate, and the reason it sits there instead of higher is the entry trigger that drops you to a single point of life once it resolves after the creature enters. The trade is structured to be temporary, not permanent, and that is the whole design tension. While the Orgg sits on the battlefield you are at one life with no margin: any burn spell, any unblocked attacker, any drain effect closes the game. But the loss is parked, not spent. The moment the creature leaves play (dies, gets bounced, gets exiled), a second trigger refunds exactly the life the first one took. So the downside runs as a clock in two directions: the opponent wants to keep the Orgg alive long enough to finish you at one, while you want to win first or remove your own creature and bank the life back on your terms. That refund clause is the part that makes this more than a flat life-payment cost; it turns the arrangement into a swingy life-total battery for any deck that can sacrifice and recur the body at will. Built around a deliberately reckless enters-the-battlefield trigger, the creature never asks whether the body is good. It asks whether you can survive the floor it leaves you standing on, and whether you control when it lets you off.
