Deep Assault

You rip open reality up to 15 feet in the air, surrounding a 15 feet radius. From the rift, tentacles squirms its way towards all creatures within radius. Each creature must make a DEX saving throw. A creature suffers 3d6 bludgeoning damage. Succeeding the saving throw causes only half damage. While the tentacles are active, the area it cover counts as difficult terrain for 1 minute and all creatures that enters and ends their turn within the radius must make the same saving throw. 

At higher level. For each spell slot above 2nd increases the damage by 1d6.