Vault CrystalHopefully your solution looks more or less like this:
Each dungeon has a number of rooms equal to the number of letters in its boss's name. Also, progress through each dungeon necessarily follows one specific sequence of rooms. In Stolim's dungeon, for example, you must go north, then east, then north (and acquire the Bomb Star), then north again to get the key to the boss chamber. Only then can you enter the boss chamber.
So you can assign each room a letter (of the boss's name) in the order in which they are accessed.
The rooms containing the dungeon items spell the answer, POLAR. Did you notice that the word "pole" can be matched up with "magnetic," "of inaccessibility," "star," "totem," and "barber's"? And "vault"???
Xaracys was supposed to be named "Xarocys," which spelled backwards is "Sycorax," the mysterious witch from The Tempest. But the one possible alternate solution (that I know of) is to swap the rooms in the top right and top left of Xaracys's dungeon, which means you can get the Totem Wand in your second or fourth room. So I had to change her name.