Ari, Master of Meta

When Ari enters the battlefield, players play a
Magic subgame, using their libraries as their
decks. Each player who doesn't win the
subgame loses one life in the main game and
each subgame and skips their next turn.
Ari's power and toughness are each equal to 2^X,
where X is the number of subgames in progress.
You may cast Ari from the battlefield of any
supergame of the current game.