MAGIC: THE GATHERING
During your upkeep, flip a coin. Opponent calls heads or tails while coin is in the air. If flip ends up in opponent's favor, Mana Crypt deals 3 damage to you.
T: Add to your mana pool. Play this ability as an interrupt.
This powerful mana accelerant is almost on par with Black Lotus and the Moxes. It is a staple of Vintage and Commander decks as well as many cubes. It ramps out spells way ahead of schedule, but beware, if you can't close out the game quickly it might come back to haunt you.