Goliath

The Great Treasure Hunter is a huge machine, it is located in the "Forest of Abundance" - Shard. You should be lead here during on of the main quests (the one that has you build a metall goliath).
This enemy has a brutal amount of HP and can not be damaged by normal melee attacks. Only ranged attacks against its head work. It's main mode of attacking for most of the fight is firing a huge barrage of missiles at you, then some stomp attacks occasionally.

I haven't tested all of the golems special attacks, so i don't know if they work or not.
But if you use your golem's guns they will likely run out of endurance and will be destroyed long before you finish the GTH.
The metall goliath has the ability to deflect ranged attacks. If you press , some energy-field like bubble will reflect shots of any kind for 1 - 2 seconds. I finished most of the fight this way by a bit of sideway kiting left and right to its head and made sure to reflect back as many of its own rockets as i could.
It still took a while and i got hit in between quite often when the shield deactivated, so bring a lot of healing and patience.