Caltrops

As an action, you can spread a bag of caltrops to cover a 5 foot area. Any creature that enters the area must succeed 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 10 feet 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.