I would be happy with a combination of:
-Fixed hitboxes on Usmash, Fsmash, Jab, Grab, Utilt, Bair, Fair (yes, they are all broken).
-Shadow Ball getting its charging hitbox back.
-Nair getting a hitbox buff so it hits small characters on startup (Pikachu...).
-Short hop Nair having no landing lag.
I feel like this is a reasonable set of buffs that would fix most of his issues. Are you fellas in agreement?
-I agree on fixing Mewtwo's F-Air, B-Air, and U-Tilt, but I think his U-Smash is fine as is, and his Grab, Jab, and F-Smash just need their hitboxes changed up a bit, not fixed.
-I don't feel like this is necessary, and I don't know how useful it would be, but I guess it wouldn't hurt.
-I'm not even sure how this works. The hitbox covers Mewtwo's entire body, so you just need to be close enough. I don't think this is an issue.
-I'm pretty sure you can already avoid landing lag on a short-hopped N-Air if you time it right.
That's just my two cents on your ideas. Personally, I'd like to see...
1. Extra power on most of his Smashes.
2. More power on his B-Throw and U-Throw
3. Hitbox fixes on any attacks that need it.
4. Maybe buff the range of his Grab so that it hits small characters more easily, and maybe do the same thing for Mewtwo's Jab 1.