Mana Vault (CE)

(This card has square corners and a gold bordered back. Not tournament legal.) Tap to add 3 colorless mana to your mana pool. Mana Vault doesn’t untap normally during untap phase; to untap it, you must pay 4 mana. If Mana Vault remains tapped during upkeep it does 1 damage to you. Tapping this artifact can be played as an interrupt.