Caltrops

A bag of 20 caltrops. As an action, you can spread a bag of caltrops to cover a square area that is 5ft on a side. Any creature that enters the area must succeed on a DC 15 Dexterity saving throw or stop moving this turn and take 1 piercing damage.

Taking this damage reduces the creature's walking speed by 10ft until the creature regains at least 1 hit point. A creature moving through the area at half speed doesn't need to make the save.