The Wonderwall

Triggered with a tune on a stringed instrument you create a 10 foot wide 10 foot tall 2-foot thick barrier of energy directly in front of yourself if an enemy makes contact with the wall the must make a wisdom saving throw, if they fail they take 1d6 psychic damage and lose an action on their next turn.

level 2 1d6

Level 4 2d6

Level 6 3d6 

And so on for every even-numbered level