Sword spikes

molten blades fill a 20-foot square on ground that you can see . For the duration, these swords turn the ground in the area into difficult terrain.

When a creature enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or take 4d6 slashing damage. A creature that starts its turn in the area makes the Dexterity saving throw or takes 4d6 slashing damage.