The series that always had some of the most entertaining bosses are the Kingdom Hearts, Zelda, Pokemon, and Tales of (later on in the game) series. Luigi's Mansion 2 has some pretty good battles as well and are challenging.
Some of the worst bosses I've faced were in fighting games.
Read my original story on Fictionpress (Shinigami Twin): http://www.fictionpress.com/s/2996503/1/Shinigami-Twin
As well as my other one (Hell's Punishment): http://www.fictionpress.com/s/3085054/1/Hell-s-Punishment
Nintendo Network ID: kingofe3