Phase potion

Phase potions were a type of magical potion similar in nature to oils of etherealness.

Powers
As their name suggested, phase potions temporarily granted their imbibers an imitation of a phase spider's ability to shift their bodies in and out of phase between the Prime Material and the Ethereal plane, making them otherwise impervious to harm on the former by all but those who could reach into the Ethereal plane themselves. The imbiber was also able to phase out with them up to of material matter. Objects could be taken without any issue, though living creatures could resist against the effect.

The effective length of a phase potion's effects was anywhere from around 8 to 40 minutes. And whilst an imbiber's body was in phase with the Prime Material, a trace of the phase potion's portal to the Ethereal plane was visible in the form of a fiery nimbus of white fire surrounding them.

Notably, the spell phase door interfered with the effects of phase potions, forcing their imbiber to remain in phase with the Prime Material for a period of seven minutes.

Creation
Creating a phase potion required either the blood of a phase spider or the concentrated juices of a rare species of tiny, button-shaped silvery white fungi that grew underground.

History
Sometime around the mid-14 century DR, phase potions were used in the North by the Cult of the White Bat, who considered them essential to their plans. Their usage of phase potions when conducting midnight enslavement raids upon isolated settlements led to their activity being reported as sightings of dwarven ghosts, appearing out of nowhere and walking through walls.