Caltrops

As an action, you can spread a single bag of caltrops to cover a 1m square area. Any creature that enters the area must succeed on a DC 15 Dexterity saving throw or stop moving and take 1 piercing damage. Until the creature regains at least 1 hit point, its walking speed is reduced by 2m. A creature moving through the area at half speed doesn't need to make the saving throw.