Simply a small tetrahedral spike. Very painful to stand on.
Caltrops
Weapon
Attributes
Unorganized
Weapon Type
Other
Weapon Class
Simple
Material
Iron
Weight
1lb (20)
Effect
As an action, you can spread a bag of caltrops to cover a square area that is up to 5 feet 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 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.