Mystery Cube

At the beginning of each player's first main
phase each turn, that player flips through the
pages of a binder they own until any opponent
says, "Stop left," or, "Stop right." Then they
choose a card from the page they stopped on and
put it into exile face down under Mystery Cube.
{6}: Shuffle all cards exiled with Mystery Cube.
Then play the top card without paying its mana
cost. Any player may activate this ability.