I find a lot of bosses are problematic because the AI doesn't know how to deal with them.
Case in point, the boar boss. Near the end when he starts going underground...
Oh, he's diving, meaning he's gonna pop from the ground and pound me for 500-1000 damage. I should just run around.
He's diving, time to block and lower that to 100-200.
*counter with B-artes combo*
*put blade back in scabbard and heal everything he just did*
Needless to say, after 10 Life Bottle I gave up keeping the AIs alive and just soloed the last part.
Same thing happened with the 2 flying bug thingy bosses. The big explosion AoE they do, I ran out of, the AIs kept sticking to them like glue and dying =/