Wondrous Item, legendary
Astral Travel. While the creature is wearing the device they may travel to the astral plane with their exact coordinates of their position in the material plane. The creature may use the device as a bonus action + half of their movement or as an action.
Overheat. Everytime the device is used the creature must roll a 1d4. On a rolled 1, the device will overheat and needs to cool down. The device will cooldown after not being used for 1 round. The creature can choose to ignore this, however they take 2d6 lightning + 1d4 fire damage.