Ruins of Adventure
These strange, iridescent fungi are native to the Ethereal Plane. Harvested under the right conditions, they can be brought into any of the Material worlds, where they are much sought after. In the Material Plane, the mushrooms remain fresh indefinitely, and are oddly tasty — their flavor and texture are typically compared to a mixture of butter and air-spun sugar.
Eating a single Multiplanar Mushroom instantly transports the eater into the Border Ethereal, as per the Etherealness spell. This shift to the Ethereal is permanent and cannot be voluntarily ended by the eater, though eating a second Multiplanar Mushroom while in the Ethereal plane will shift the eater safely back to the Material.