Donkey Kong is fairly balanced. His main problem is that speed characters have more advantages. (Fox and Marth have a powerful smash rivaling the big guys; Fox and Captain Falcon can survive vertical hits easier then the giant monkey). Otherwise, DK needs only a few improvements.
1. His Forward Aerial has enough lag time to warrant more power.
2. His Forward B should either be changed to another move or it should come out much quicker. It is useless as it is. (I would opt for DK to have an upgraded, swifter head butt. I think the monkey should have the biggest collection of meteor smashes and spikes, although not necessarily the best ones).
3. He needs his somersault roll from his games. Perfect move for the dash attack.
4. DK should be the king of meteor smashes and throws. As it stands his throws are great, but his grab is horrible. The short-range balances out his throwing capabilities, but that doesn’t mean his grab cannot be improved slightly. My idea is that DK reaches out with both arms on either side when he grabs. The range is short (same length as current grab) but hits both sides to grab rollers. Also this lets him grab two characters at once. Pressing A smashes the opponents over his head, into each other for 10 percent damage each (it is rare that you would get two people) and then would toss each in the same direction. Both can be carried.