So after many deaths, we finally figured out how to beat the invincible Guru Aych'tu'oh. It sounds simple but hard to pull off when everything is in chaos. It requires teamwork and a stroke of luck.
1 Bear: Gets and maintains Aggro (dies a lot lol! I'm sorry)
2 Mage (wand/bracer): "timed" heals in between damages, 1 mage cannot catch up, you need 2 healers. Dispose mob quick, get aggro of mob while on shield. Potion is disabled in this dungeon, so the party will rely on mage's ability to heal properly (i.e. don't heal when everyone's full)
2 Birds: damage dealers focus on boss, don't try to get aggro of mob, you'll die instantly. Avoid casting aoe spells so you don't get mob attention, just single enemy dmg skills on boss.
1. Bear comes in first, gets boss' aggro, and leads him to one of the corner pockets
2. The bear's job is to make sure his aggro stays with him
3. Mage, time your heals, specifically looking at the Bear's HP, don't let your bear die.
4. Death of the bear situation: If the bear dies, birds should instantly stop attacking and mage should revive quickly and puts on mana shield. If birds were quick enough to retreat, the boss will shift aggro to a "shielded mage", both mages can then heal each other while waiting for the bear to resurrect. Once the bear is back in action, let him take back aggro by still "not attacking". Bear should be quick on his fingers and cast taunt right away once revived and just spam everything else. Once bear gets back aggro, it's back in business. Don't panic and don't run away.
5. Back on track, birds just putting all the hurting unless there's a bear death situation
6. Mage focus on reviving the bear (the bear will die a lot, refer to bear death situation)
7. If you do this successfully, nobody in the team will die except the bear (LOL!)
8. Unintentional Stealing of Aggro Situation: If at any point a mage/birds steals aggro from the bear even if the bear is not dead, chances are that mage/bird will die because things will happen too fast and he will not know he took aggro before it's too late, don't fret though, as long as you have one mage standing, you will get rev'd, so don't be afraid to die. Bear should try to regain aggro as quickly as possible to stabilize the group. Don't run away. Keep the boss in the pocket corner.
9. This is where it gets tricky, when the boss screams, he will then go for a random tower (I'm not sure if it's random)
10. He will get his health healed 100% (even if you managed to bring down his health significantly) if he gets near the tower and be invulnerable for a short period, he will also emit an AOE attack like Aunt Emma that hurts a lot if you're anywhere near him and will push you back, this will cause you to be out of range to heal or be healed...in short, don't go after him when he's already near the tower.
11. Now, when he screams, TRY TO GET IN A MEGA COMBO AS QUICKLY AS POSSIBLE!!! There are three kinds of mega combos, any of those should work. This is the primary reason why you need him in a pocket corner, because if you're in a pocket corner, the distance between him and the next tower will be greater giving you more chances to get in that mega combo. The second reason for that pocket cornering is that it will allow the team to dispose the mobs quicker because it's in a small enclosed area. You need to dispose all mobs before the boss screams otherwise, they will disrupt the harmony of your team (mobs can stop you from your tracks when they hit you, they can also push you across the map, like a slingshot beckon) during the process of chasing the boss and chances of making a mega combo goes down.
12. If you successfully hit the boss with a mega combo when he's on his way to a tower, he will stop running and sort of become stunned...
13. You can all now put the beating on him...
14. If you have at least 3 people in thrasher in your party, he should die before he can scream again, if not....
15. Go back to step 1 :P
PS and probably the most important tip: For Mage your crucial skills to create a mega combo is "ice", "lightning", and "drain". For birds, "root" and "break armor". Bears, "Hell Scream" ,"Stomp", and "Crushing Blow". Cast in that order, you should get one mega combo in. Don't overthink the order, you will end up panicking, and end up forgetting about the entire gameplan. Just cast those skills "IN ORDER" repeatedly and hope for the best (this is where the luck comes in) :P Also, the reason I say "don't run away" is because the team should be within range when the scream occurs so you can all contribute in the execution of the mega combo. If one is out of range...the chances of getting a mega combo goes down (the boss walks fast when he's going for the tower, around as fast as someone with thrasher).
PSS: Without the right strategy, even if everyone is in thrasher elixir, your team can fight this boss forever and not beat him :P So, the battle could end in less than a minute, a couple of minutes, or drag on for an hour until you give up, depends on how your team executes the gameplan and how many of you are in elixir (thrasher or the other variants).
Note: The boss is not impossible to beat without using platinum elixirs only gold purchased elixirs. I was in a team where only one was in thrasher elixir (a dex bird), the rest, using gold purchased elixir (melee and armor), and we managed to beat it using this strategy. The battle was a lot longer, more deaths, and it required repetitive and consistent execution of the mega combo (one mistake means back to full health boss O.O). Let's see if I can find a team that can beat it with no platinum elixir at all. (when I get home from work, 'till then :P)
Good luck! :P