Grunty from banjo-kaz was alot of fun to battle, complete with witty rhyming lines and all. If you liked the original BK try get banjo-tooie, its got a really nice reply feature so you can battle or replay your fav parts of the game without having to play it right over again.
Hardest boss? I would say dessan from JK2. After flying through the game on Padawan i decided to up the anti and put it on jedi master. Cant anyone say "lightning whore"
didnt even get close to him, he just fried me over and over.