Wondrous Item, uncommon
This bag contains 1,000 magic marbles. These marbles can take any pattern, design, color, or transparency you chose without being completely invisible. They can also shed dim light of any color for up to 5 feet if you so wish. You may use a command word as a bonus action to summon the marbles back into your bag. Upon saying the command word, the marbles pop out of existence sporadically like bubbles and instantly appear back in your bag.
As an action, you can spill these marbles from their bag 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 12 Dexterity saving throw or fall prone. A creature moving through the area at half speed doesn't have to make the save.