Play solo as Diddy Kong. While an amazing game, it is rather disappointing that you can't actually use Diddy Kong alone in single player. Well, I had a thought that ended up a working, very simple remedy. :)
How to perform: It's quite easy, all you have to do is go to co-op mode, and, while this may seem rather mean, you simply get rid of Donkey Kong and you're left with Diddy to play alone so as long as you set Player 1's controller aside and don't press the A button. Diddy is really fun to use alone. :)
If you die with Diddy, you'll have to repeat the process. However, you won't lose any lives unless both Kongs die.