Yawgmoth's Puzzle Box

When Yawgmoth's Puzzle Box enters the battlefield, exile all graveyards.
At the beginning of each player's draw step, that player discards their hand and draws that many cards. Until end of turn, they may cast cards from their graveyard.
If a card would be put into a graveyard from anywhere and was not put there by Yawgmoth's Puzzle Box, exile that card instead.