Flippy, Master of Chance

Before a player taps for mana to cast a spell, they
may flip up to X coins, where X is twice the spell’s mana cost. For each win, that spell costs {1} less.
For each flip they lose, Flippy deals 2 damage to
them for each coin flipped for this spell, and the spell costs {1} more to cast. (For each X in a spell's mana cost, flip up to 2 additional times.)
{p/u}: Redo a coin flip. Any player may activate this ability at instant speed.

"Using Even or Odds works, too."