Vault 14 is a secret vault. Mikayla and Mason tried not to let Brady and Boomer find out about it because it contained dangerous magical items like the Screechy Giki, Duplicatus Plantis, a lie detector and invisible sword. The code to open the vault is 118, and was intended to have only been known by Mikayla and Mason. About 50 Brady and Boomer copies and one Mikayla copy rest here.
It appears in the episode The Trouble With Doubles.