Shipbreaker Kraken

The eight-mana monstrosity activation is the toll, and it buys something most blue finishers do not: a permanent shutdown of four blockers. Tapping creatures is cheap; keeping them tapped is the rare part. The lockdown clause turns a one-time tap into a standing soft-removal effect, freezing up to four bodies for as long as the Kraken survives, which reframes the activation cost as the price of removing the opponent's defensive grid rather than just clearing a single attack. That ties the card's value to its own presence on the board: lose the now-monstrous 10/10 and the locked creatures are free to untap at their next untap step, so the effect is only as durable as the body carrying it. The two-mode structure (a 6/6 body until you have the mana to pay, then a 10/10 that strips the board open) makes it a top-end card that does little on a tight curve and everything once the game goes long. It belongs to a school of monstrosity design where the activated half is the whole point and the base body is a placeholder: the card is built to be flooded into, not cast on schedule. The tap targets are chosen when the triggered ability goes on the stack, after monstrosity has already resolved, so you size up the battlefield with the counters already on and the lock lands exactly when you are ready to swing through an emptied board.