Here's my Pac-Man stage idea. Take the borders and ghost box and sink them into the background, like the bottom of of 75m. You get a playfield that looks like this:
An alternate is to only use half and cut off at the ghost box.
I love the Power Pellet Final Smash idea. For his up special, I think he should turn into his pixelated form and have free-movement for a few seconds. He starts going up, but if you press left, right, or down, he goes in those directions as well just like in the classic game.