Moonlighter

Good thing to keep in mind when fighting the Golem king, is you that don't take any damage when using your big sword charge attack 'K' (on computer) so you can fight right next to him. you just have to time your attacks right and it's quite possible you may get a perfect boss fight but your timing has to be precise.

I had a full steel armor set (it's the basic heavy armor)
Big Sword (+1 upgrade also enchanted)
5 potions (just in case)