Here, have a picture of Kappa and Foxie as Sonic the Hedgehog characters. Why not?
They probably wouldn't be all that speedy: if they were playable characters, I imagine Kappa's skill set would mirror Knuckles' pretty closely, and Foxie would be like Amy Rose.
Of course, I haven't actually played any Sonic games myself--I've only watched others play them! But Knuckles is still my favorite :3
Neither Kappa nor Foxie typically wear shoes, so I just made them up some, since a vast majority of Sonic characters wear some type of footwear.