Diddy’s smash moveset needs some subtle but substantial tweaks. Mostly to his specials. He’s not a tricky monkey like run of the mill chimps in cartoons. He’s a brash and headstrong guy who’s desperate to prove himself a true hero and has automatic weaponry. He should be more aggressive and chaotic, not calculating and planning.
His neutral special can still be Peanut Popguns but they need to work differently. Instead of firing it once and being able to charge it, how about he pulls out both and fires a quick shot from it, and mashing the button allows him to rapidly fire from both guns. He can’t move while doing this though. Maybe even give him a limited ammo pool, but I’m not sure about that.
His side special should now be his Chimpy Charge ability from DK64. He just charges forward and headbuts whatever he comes into contact with. But if it’s not an enemy he ends up in a vulnerable position.
His up special can still be Rocketbarrel Boost, but again, instead of charging it, he just rockets up. Maybe he can even freely fly around as long as he holds the button down, but he has a limited fuel meter that runs out fast. While flying, pressing a lets him shoot from the peanut popguns, drawing from the same ammo pool as his usual neutral special.
His down special can be the orange grenades from DK64. Thrown forward in an arc and exploding on impact. But again, drawing from a limited pool of ammo.
His final smash, Guitar Guzzump. I suggested something similar for DK a while back. It’s a screen nuke, it damages everything on screen. But the damage is stronger the closer you are to Diddy and weaker the further away you are.