@Weegee: sure, feel free to suggest any moves you want

the ones I posted were poorly thought out stuff that I just through together in a matter of two minutes. And I only picked darkness and electric simply becuase Boo is a ghost

Ok, here's my ideas--not saying that yours are bad.
King Boo is a ghost, and what are ghosts? Sneaky and tricky. I think King Boo should be a tricky, unpredictable character, with lots of surprising moves.
Let me demonstrate with some ideas:
-Your side B: I think it fits this pretty well
-Down B: Like Metaknight's
-fsmash: a body slam forward, but to add an unpredictable spin on it:
-if you tilt it up, he should do a flip upward while moving forward, and then hit the ground. It takes longer, to mindagame people who would've spotdodged
-if you tilt down, he'll move up a bit, then swoop down in a curve quickly, the fastest variation.
-no tilt: He slides forward normally.
Things like that, but I didn't have much ideas.
could you be able to lengthen the vertices on the rear of king boo to give it the ghost tail
I was thinking of that too.