This video goes over the basic strategy for fighting bosses with a Ninja.
Lure the boss around an object, stun, attack, wait for cooldowns, repeat. This will work for all bosses - even ranged ones (as they can't attack you if you're standing behind an object such as a well).
Let me know if you guys have any suggestions. I know the audio is messed up - it's not balanced correctly. I'll try to fix that in the next episode.