Not sure about Specials, but Wario's attack speed would go a long way toward making K. Rool a viable contender at a higher level.
If anyone has any great ideas for K. Rool's specials, be sure to submit writeups detailing them. I've put in the Kredits Final Smash and Death Rool already, heh.
Very well then!
So let's see.
NEUTRAL B
BLUNDERBUSS 1: BALLS ONLY, FINAL DESTINATION
To differentiate from BJ, the kannonballs cannot be charged up. Instead, they are spiky and drop fairly early. To make up for the fact that they don't go very far, they instead extend the spikes, like in DKC2, becoming nasty traps that impede the movement of enemies. Essentially bananas, but nastier overall. Up to two balls can be placed at once, after which the blunderbuss will just whiff. Standing next to the balls and pressing B will quickly suck them up.
The kannonballs may also retract their spikes after a while, however, making them throwable items (or perhaps more akin to footballs, hitting them moves them about).
BLUNDERBUSS 2: BALLS+GAS
Same as above, but with only one kannonball out at the time. When the kannonball is out, K. Rool can fire clouds of gas. I'm not sure what the status effect of the gas should be, freezing would work quite well because it already is a status effect and its effectiveness scales with the damage taken by the victim. Slow seems kind of nasty, but I think it'd fit better with K. Rool overall. Switching controls is cruel and I don't think we should do that.
BLUNDERBUSS 3: BALLS+VACUUM ON COMMAND
More in line with the bossfight. Like 2, only one ball is out at a time, but instead of firing gas the blunderbuss will start sucking things in a la pink puffball. It'd be akin to Villager's pocket, but only with thrown items and projectiles. The item can then be fired at a higher set velocity with no dropoff.
CUSTOMS: Either bouncy balls or spinny balls. Or just make those three custom variants.
Personally I'd go with either first or second version as the neutral B. Two balls are much more pressuring than one, and offers more of a focus on trapping. However, the gas attack offers much more utility. I'm not sure how I feel about the vacuum, it's more the Villager's schtick.
I'm uncertain what to do with the other B's.
Up B could be the helicopter thing. I'd like to have some sort of hoist-by-his-own-petard thing going on, reflecting on the way you defeat him in the games. Attacking the backpack makes him drop out of the sky. Alternatively he could fly on his blunderbuss, which is way sillier.
Side B could be krown toss, but it doesn't really offer a whole lot other than being a projectile to have out while you can't shoot balls, in which case it would work best in combination with BLUNDERBUSS 1. Maybe he suffers from more damage from above while the crown is gone? I'd prefer not to be honest.
Down B could involve the falling cannonballs, or invisibility. Either could work really.