Pineapple Upside-down cake!

When this card enters that battlefield, each player flips all cards on their field face down. Then, each player flips their decks upside-down.
All face down cards are treated as 0/2 muffins with the ability "{t}, put a card from the top of your library onto the field face down"
If a player controls 11 or more muffins, that player flips all their cards face up and takes 1 damage for each. If this card leaves the battlefield, Shuffle together all face down cards.