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Whenever one or more creatures you control deal combat damage to a player, create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
At the beginning of your end step, if you control five or more artifacts, transform Storm the Vault.
For more information on double-faced cards, see the Ixalan mechanics article (http://magic.wizards.com/en/articles/archive/feature/ixalan-mechanics).
In a Two-Headed Giant game, if you control more than one creature that can attack, you attack different opponents so that Storm the Vault’s first ability triggers twice.
Storm the Vault’s first ability can trigger more than once in a turn if creatures you control deal combat damage at different times in a turn (most likely because one or more has first strike) or if creatures you control deal combat damage to more than one player at once.
The last ability of Storm the Vault doesn’t trigger if you don’t control five or more artifacts as your end step begins. If it does trigger but you don’t control five or more artifacts as it resolves, it does nothing.
