Break the Web

Specially last 2 rounds will be hard if you don't know what you are doing. Simply, use this approach and be patient:

1.Get close to the boss until it starts to shoot you.

2.Immediatly start to move straight&backwards as you keep your finger on the left click of your mouse (Spam attacking with your Katana, this will make you avoid ALL of the attacks and send them straight back to the boss)

3.Repeat until the boss is dead.

Always face directly to boss as you move forward and backwards. This approach is 100% successful if you do it correctly. It works with every mob you have trouble with through the game.