Rune-Scarred Demon

Demonic Tutor stapled to a 6/6 flyer is the whole pitch, and it works because the body and the search both want to cost more than the bare spell. Demonic Tutor was famously undercosted at two mana; here the tutor is rebuilt as an enters-the-battlefield trigger, so seven mana buys an unconditional library search and a flying clock that ends the game before the fetched card has to. The trigger structure is what gives it staying power across long games. Anything that flickers, recurs, or reanimates it re-runs the search, turning a one-shot tutor into a repeatable one and a 6/6 into a chassis for value loops. The card the search finds matters more than the demon: a single black creature can fetch a combo piece, a board wipe, a missing land, or another threat, then stay on the table as a beater that demands an answer. The cost is the only restriction worth naming, and it cuts in a specific way. The trigger itself is bulletproof: it hits the stack the moment the Demon lands and resolves whether or not the Demon survives, so a removal spell in response still leaves you holding whatever you searched for. What removal denies you is the clock, not the card. Seven mana buys immediate, unconditional card selection now and a threat later, and the second half is the part an opponent can actually take away.