Ponder, the Demon of Decisions

{u}{r}{g}{t}: By exiling {x}cards from their graveyard,
any player may return a card with {x}mana value to
the top of their library.
Whenever a player makes a "choice", they may select another player. If an unchosen option remains, the selected player may activate an unchosen mode
without paying any additional mana costs.
Ponder costs {1} less for every instant and sorcery in
your graveyard with different mana values.