No real 'key'. Consider this your first challenge. He's pretty easy. The only 'key' to bosses are learning what moves they do so you can prepare for them. Many attacks, you can block. Some, you just have to get the fuck away from. Some will one shot you if you get hit.
Just a matter of learning them, and being precise enough to not get hit by them.
I'll give you a hint and say that the 'falling attack' is pretty helpful in some fights. You won't get many opportunities like that though, so don't think you'll have that ability every fight.
|