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Power / Toughness:
Mana Vault does not untap during your untap phase. At the end of your upkeep, if Mana Vault is tapped, it deals 1 damage to you. <4>: Untap Mana Vault at end of upkeep. Use this ability only during your upkeep. <T>: Add three colorless mana to your mana pool. Play this ability as a mana source.