Azmar's stone spikes

You reshape the earth and stone in a point within range. In a 20 feet square within that point jagged spikes of stone burst through the ground. The spike are 5 feet tall. Any creature in that radius needs to make a Dexterity saving throw. On a failure they suffer 8d8 bludgeoning damage, half on a success. The ground in the area is difficult terrain. Any creature that walks through suffers 5 point of slashing damage for every 5 feet of movement.