Marbles

These tiny round balls are made of polished stone and colorful glass, and come in a bag of 200. You can pour marbles in an empty square adjacent to you with an Interact action. The first creature that moves into that square must succeed at a DC 13 acrobatics check or DC 13 reflex save (its choice) or fall Prone. Once a creature enters a space with marbles, enough marbles are scattered that other creatures moving into that space don't need to attempt a roll to avoid falling.