Medomai the Ageless

The extra-turn engine, leashed at exactly the spot where extra-turn engines run amok. A repeatable Time Walk on a flying body should be a runaway loop, and the design knows it: the clause forbidding Medomai from attacking during those extra turns is the whole governor. You get the bonus turn, you spend it untapping, drawing, building, swinging with everything else, but the Sphinx itself sits the dance out, so the second hit can never come from the same source that bought the first. That single restriction converts what would be an infinite-turn lock into a tempo lever: every gifted turn is one you have to cash out through other threats while the six-mana evasive body waits to connect again next combat. The flavor reads cleanly into the rules, too, a prophet who sees ahead but cannot personally seize the future twice in a row. The build-around tension is whether you can punch through often enough to keep the chain alive without the Sphinx becoming a liability the turn after it lands. It wants a board that does damage on its own and protection that keeps an unblocked attacker unblocked, because the entire value proposition collapses the moment combat damage stops landing on a player.