Bigby's Acid Wave

A large wall of dark green acid appears right in front of you thats 15 ft. tall, 15 ft. wide and 1 ft. long.
You send the wall of acid as a wave over all creatures in a 25 ft. long, 15 ft. tall and 15 ft. wide cube in front of you.
Each creature in the area must make a Dexterity savingthrow.
On a failed save, a target takes 6d6 acid damage and has it's walking speed reduced by 10 ft. for one round. On a successful save, the creature takes half damage, but suffers no other effect.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 3rd.