The vault is a record of the various monsters , weapons , items , and dungeon objects that have been found in game and used by either the ghosts or the hero. The Vault provides a description for almost every object, weapon, and item.
As of the 0.8 update, monsters are unlocked in the Vault after playing as them at least once. The Vault does not give specific information about the monsters, but it does allow a special practice mode for unlocked monsters. This mode involves playing as a selected monster against a bot Hero, who respawns every time he is killed and gains a point in Vitality, Strength, and Agility as well as new equipment after each death. In addition to recording the record runs for each monster, the game also records the total of all of these. Each monster has a set "goal" for how many rounds that the monster can survive. Generally, reaching the goal means that you are proficient enough in using that monster to be a fair match for hard mode bots. Once a goal is reached, a checkmark will appear next to the monster in the Vault screen.