The Vault is an invisible reward system that triggers every time you get a fifth copy of a card. Since a fifth copy of a card is useless for the players, the Vault is (currently) Wizards’ solution to the fifth card problem.
The Vault opens up when you have accumulated 900 progress points. It rewards you with:
- 1 Mythic Wildcard
- 2 Rare Wildcards
- 3 Uncommon Wildcards