Bag of Infinite Ball Bearings

This small bag is full of tiny metal balls that audibly rattle slightly when the bag is shaken.

As an action, you can spill these tiny metal balls from their pouch to cover a level, square area that is 10 feet on a side. A creature moving across the covered area must succeed on a DC 10 Dexterity saving throw or fall prone. A creature moving through the area at half speed doesn't need to make the save.

At dawn, any ball bearings that have been expelled from the bag turn to harmless smoke and vanish, the bag then fills back up with ball bearings again.