Controls mapping is nice, but you can also check for which side is the wall and make the arrow of the same direction cause the shrink and that of the opposite direction to cause the flip.
You can get the wall's direction from the character's current rotation and use them; for example if the wall is at the bottom then Down/ S button will cause shrink and Up/W will cause Flip and so on, and dash can be spacebar or the current movement direction.
Also a small script attached to each wall object with a variable defining the wall's direction and when you click an arrow/ WASD button you first check for the wall's direction from that said script and then make the effect depending on the retrieved direction.
I'd also like to see a version where I can move on my own and fight the enemies that will come out form every direction and try to overwhelm poor Cubey :D