Null Chalk (Patreon)

Wondrous item, very rare

This drab pouch contains 1d4+1 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 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 targeting 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 would cross the line on its turn, that creature must make a DC 17 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 2d8 force damage. On a successful save, the creature's speed is unaffected as it passes through the line and the damage is halved. 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. The line uses a DC 16 ability check DC when targeted by a dispel magic spell. On a success, the line's effects are disabled for 1 minute.

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