I've been thinking about a game like that for quite a while, mostly because I'm a sucker for fighting games
These are just a couple of ideas I had about the roster, as well as how each character would play out (this is gonna be a long one):
Klonoa: I thought about 2 different ways Klonoa would play out. Either he'd be a speedy fighter who trades damage for maneuverability, or he would be a stance fighter who takes advantage of his weapon set from Klonoa Heroes, with a different set of moves for each weapon that you can switch, or even cancel into
Guntz: The most obvious playstyle for him would be a
spammer zoner, taking advantage of his firearms to control, bait, and punish his foe
Lolo + Popka: I thought it would be much more fitting to have Lolo and Popka fight together as a pair, much like the Ice Climbers in Smash
Pango: Bombs, plenty of bombs
Leorina: I think she would be somewhat similar to Klonoa, as she would be using her fake ring, but she'll be slower and harder hitting. And knowing that she can create monsters in LV, she would use them to assist her as well
Tat: I haven't thought of any specific playstyle for her, I just figured that she could use her ability to split in 2 to her advantage
Joka: Obvious trickster fighter, seeing that he's a clown and all.
Janga: He could be a bit of a zoner himself, because his claws are freakin' huge, but he would also have the ability to dish out gradual effects, such as Poison and Slow
King of Sorrow: With his Nemo Moos, I think he would be a great charge fighter, as he would be able to charge up his attacks for higher damage, as well as cancel out of them for follow-up attacks
That's about it for now. I hope this will help out at least a little bit