Share the Spoils

When Share the Spoils enters the battlefield
or an opponent loses the game, exile the top
card of each player's library.
During each player's turn, that player may
play a land or cast a spell from among cards
exiled with Share the Spoils, and they may
spend mana as though it were mana of any
color to cast that spell. When they do, exile
the top card of their library.