Just a little update. The boss can also use Meteor Strike, Ranged Attack (where does he pull the arrows from. . . He's a giant piece of armor with no weapons), Magnum Shot, Mirage Missile, Judgement blade, and Celestial Spike. He also uses that one Girgashiy skill that immobilizes the player in crystal. He can summon clones of you to fight you. There's some skill that makes purple circles on the floor but idk what skill that is. He spawns with Cobweb Ghosts, Goblin Hunters, those Goblins that look like monkeys, Skeleton Ogres, and Castle Golems. All with tanky health. He doesn't have advanced heavy stander so if you annoy him you can interrupt his charging animations. He also changes the color of his ponytails, I've noticed him be Blue, Green, Red, and Gray. Idk what his color does yet but as I said, it's probably a Nightmare-deal. He also can teleport halfway across the arena, which is a huge distance. What skills/abilities he has probably varies with difficulty. He could use better AI/larger aggro range. But still, I'd suspect most people here would have trouble in at least the hardest difficulty of this boss if not earlier.
People were mostly going hit and run because they can't handle this boss, from what I've seen. The only "typical" tactic they used is trying to clear out all the mobs then corner him at the door frame (have to be very exact because the door frame isn't very wide) so they can spam way of the gun on him.
Edit: For the laughs
[Image: http://ft.trillian.im/d8946682d6c7da7bef24121282783a3ada1b2a88/6whyFrU4fApIK3GXIHOmic5ZLegQs.jpg]
Edit 2: I forgot to mention he also very rarely normal attacks (looks like he's shoving the player out of the way). That's the only melee I ever saw him use, unless you count Judgement Blade as melee.