Karn's Temporal Sundering
The extra turn is created first, then the bounce lands, and reading those two clauses in that order is exactly what makes the spell a finisher rather than a setup piece. You grant yourself the extra turn, peel an opposing blocker or planeswalker off the board on the way out, and then the bonus turn arrives on schedule after the current one closes (standard extra-turn timing, nothing exotic). The untapped attackers you leave behind meet an already-thinned defense. The gate on this class of spell wants a marquee body already on the board before you can cast it, and it is specific about that body: a legendary artifact, land, or enchantment will not open the door, only a suitably storied creature or walker. That turns the six mana into payment for a payload you were supposed to have earned by committing a headliner to the board, not a tool you spin up cold. And the self-exile at the end does the heaviest design work. Repeatable extra-turn effects are among the most volatile engines in the game, the kind of thing that ends matches sideways in a loop; removing the card from existence after a single resolution forecloses that entire category of abuse. One tempo lurch, never a chain. What sits underneath is an extra-turn effect built for a board that already tilts your way: a closer for a legend-heavy deck that wants to be ahead and press the advantage, priced and prerequisited to reward that commitment rather than bail out a stalled position.
