Potion, very rare
This swirling silver potion gives off a ghostly vapor that seems to fade in and out of the bottle’s surface. It feels unnaturally cold to the touch, and its magic is clearly unstable. Once brewed, the potion loses its potency within 1 hour if not consumed.
When you drink the Phantom Draught, your body becomes partially incorporeal for 1 minute. During this time, you can move through solid objects as though they were difficult terrain. You cannot end your turn inside a solid object. If you do, you take 5d10 force damage and are shunted to the nearest unoccupied space.
While phased, you appear translucent and ghostlike. You can’t manipulate physical objects not worn or carried, and attack rolls against you are made with disadvantage.
The potion radiates strong conjuration and transmutation magic. A DC 15 Arcana check reveals its instability once unsealed.