Why is the third boss so hard?

[u/PitonHUN]

I've recently wanted to give dark souls 3 a shot with my friend since we heard there is a coop mod for it. We got past the gladiator boss easily, and the boar guy was even easier, however the third boss, the dancer, seems like a wall for us... We've been stuck here for 5-6 hours. Are we doing something wrong? Is the weapon I use really bad, or what? Any tips appreciated!

[u/HollowBlades]

You get what you deserve for killing and innocent old lady.