Caltrops

You spread metal caltrops in a 5-foot cube within range. When a creature enters the spell’s area for the first time on a turn or starts its turn there, it must succeed on a Dexterity saving throw or take 1d4 piercing damage. Taking this damage reduces the creature's walking speed by 5 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 and takes no damage. If a creature's walking speed is reduced to half its maximum or less, the creature no longer triggers the Dexterity saving throws and can take no additional damage from this spell until regaining at least 1 hit point.