Null Chalk

Wondrous item, very rare

This drab pouch contains 5 sticks of dull gray chalk. The chalk feels slightly tingly to the touch.

As an action, you can touch 1 of the sticks of chalk to the ground, wall, or ceiling to magically create a line that is up to 50 feet long and 1 foot thick. The line extends from your location in the direction and shape of your choice. You can shape the line in any way you choose so long as it makes one continuous path along the surface or similar adjacent surfaces. Once a stick of chalk has been used in this way, it disintegrates into a pile of fine, nonmagical powder.

Magical effects can’t cross this line. The line’s effect extends 20 feet perpendicularly from the surface on which the line is drawn. Targets on the other side of the line are considered to have full cover for the purpose of being targeted by spells or magical effects. Magical items that cross the line become mundane and nonmagical for 1 round.

The first time a celestial, elemental, fey, fiend, or undead creature attempts to cross the line on a turn, that creature must make a DC 20 Charisma saving throw. On a failed save, the creature’s movement speed becomes 0 until the start of its next turn, is forced backward up to 10 feet away from the line, and takes 8d8 force damage. On a successful save, a creature takes half as much damage, and its speed is unaffected as it passes through the line. If the line cuts through a creature’s space when it appears, the creature is pushed to one side of the line (your choice).

This effect lasts for 8 hours or until a break of at least one foot is made in the line, which causes it to instantly lose all magical properties. A creature can spend 1 minute to smudge, smear, erase, or otherwise remove the line enough to disable its effects. When targeted by the dispel magic spell, the line is treated as if it were a 6th-level spell. If the line is dispelled in this way, its effects are disabled for 1 minute.

Also good for upset stomachs. Well, maybe. I've never tried it.