wow.... i accidentally started with just the basic arrow and no charm and I killed the boss easily. this doesn't even need a guide... And I didn't know about the stalagtites, so I just shot him repeatedly.... fail.
No, all you need is the life regenerating charm...Don't have have to worry about anything. The boss can't deal enough damage if he backs you against the wall...either that or he can't hit you. One of the two.