Tungsten Terrain

Tungsten spikes erupt from the ground, forcing all creatures within a 30-foot circle within range of the caster to make a Dexterity saving throw, on a failed save, a creature is knocked prone. All creatures, excluding the caster, within this radius must spend 5 feet of movement fore every 1 foot it moves. 

On subsequent rounds, as a bonus action, you may force a creature within this terrain to make a Dexterity saving throw, on a failed save that creature is knocked prone.