Torchlight 2 Walkthrough Part 15: Breaking The Siege
When you are ready to begin this quest, leave Zeryphesh and head to the Salt Barrens. From there, proceed to the Witherways. This area is infested with what are called artifact creatures. Basically, these guys will be hitting you with a lot of electrical attacks, beings of metal and electricity as they are. They also have the tendency to use ranged attacks against you. Use towers and turrets to fight them with their own game.
When you reach the lair of the Siege Guardian, buff your pet up with a Vampiric ability if possible, or give him a fish that will boost his attack power up high. The Siege Guardian is a massive mechanical creature who attacks with spinning drills and other mechanical bits. Being made of metal, this guy has some serious endurance and defense, so prepare yourself for a long battle when you enter.
As the battle begins, keep a close eye on the Siege Guardian to tell which attacks he is about to whip out on you. He typically alternates between two methods of attacking. The first method is a normal, straightforward pummel attack. Avoid this one simply by dodging to one side or the other. The second attack is a fast sweeping charge attack. This one is much tougher to avoid given that it is relatively speedy. Sometimes you can duck behind one of the pillars in the arena to avoid the sweep attacks, so keep this in mind if things start to look perilous.
A good strategy to use in this fight is to boost up your elemental defenses using magic. Eventually, the Siege Guardian will lay down some turrets. Ignore them, let them hit you as long as you have your elemental defenses up, and just keep wailing away on the Siege Guardian himself. As mentioned earlier, this is primarily a battle of endurance, but the Siege Guardian will fall eventually with repeated attacks.