>>13710394
>>13710209
I like this idea, but to expand upon it further, I'd give Tails not only the ability to fly, but special gadgets to use. I feel like they restricted him too much in Sonic Adventure 2 when they just put him in a mech and let him go. You could seriously add some really silly gadgets, such as a portable spring, an extending boxing glove, maybe an explosive charge; in general, each gadget would need to serve a specific function, either in exploration or in combat, that would give him advantages that Sonic and Knuckles wouldn't have. Between the flight and a portable spring, Tails would be able to reach the highest platforms and paths neither of the other two would be able to reach; his combat would be mostly at range with gadgets and tricks.
As far as Knuckles goes, I'd say his ability to dig and knock away certain walls and obstacles would definitely stay. He'd have the ability to climb most walls and glide, and he would have explosive melee combat. Knuckles should ideally be able to glide much longer distances than Tails would be able to reach without getting as high.
Of course, with his speed, Sonic would be able to travel certain paths, such as running across water surfaces, certain walls and shuttle loops where certain ones with leading slopes and/or boosters are used by everyone, and 'combat' would likely be the same platforming-style baddie bashing to get to the other side it's been for a long time.