Venomdust

You touch a surface and a small pile of 1d4+2 pinches of powder appears, one pinch is enough to coat a medium or smaller object, when a creature is hit with an object coated in Venomdust they must make a Constitution saving throw, on a failed save the target takes an extra 3d10 poison damage, on a success they take half the damage. After one hit the dust vanished from the weapon, and once the duration is over all the dust vanishes.