The only actual answer anyone can give is "we don't really know yet" because... we don't. It's not stated anywhere.
Anything anyone else said is just guessing or conjecture.
I did the doomhammer legendary questline on beta along with all of the order halls and most of the other legendary questlines. Of all of them, the doomhammer one was the one that really stood out as a very weak storyline. That line just really makes little sense and is really mediocre. In a nutshell Thrall who all along has been one of the more powerful and important characters in all of wow lore, suddenly and for nonsensical reasons has the elements mad at him. So he has a "feels bad" moment, says he needs to go away and ponder life, and that's that. You come away from the whole thing like, huh wtf was that? The guy who helps save the world from Deathwing suddenly is emo?
The elements are temperamental children, the Draenor elements left messages in the Doomhammer. The Azeroth elements read this and said 'Mother fucker!' They are pissed at Thrall for the same reason the water elementals came bitching to him about Jaina. They feel she is abusing them, plus Thrall doesn't admit that he has made mistakes! Nope everything that happened is because of Garrosh and only Garrosh. And this duel where we pick one weapon I cheated in, cause the elements consider themselves a weapon. So when he lost his smashy thingie and then used us that was totally unfair. So fuck this guy, earn our magic mojo back!
Well basically he was flying above the moon, fighting Nick Fury, who it turns out was kind of a nut job... Then just before he could land the final blow, Nick leant in and whispered something to him, some dire secret, and now he's no longer worthy to wield his hammer.
Oh...
Wait...
Sorry, wrong element wielding hammer guy with performance issues!
Thrall's powers are on the fritz for a few reasons, but what seems to ME to be the most likely and also interesting, is that even though Garrosh was a colossal asshat, thrall feels great remorse for how everything ended. This, coupled with them wanting to write Thrall out and give the Doomhammer to enhance lead to him getting a whack with the nerfbat (for a similar situation, see Tirion and the Ashbringer).
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As has been said before, he hasn't lost his powers. He has lost the ability to hold/wield Doomhammer properly. He says ever since he defeated Garrosh that it has felt heavy in his hands. As far as I know, Doomhammer is basically shaman mjolnir and has deemed that Thrall is no longer worthy, and we, the shaman hero are.
It is. Magic is banned, save for one shamanic blessing on your weapon. Gul'dan is similarly condemned during the Warcraft movie for using magic during a Mak'Gora. He cheated. Honestly, I think Blizzard forgot that was cheating, just like they forgot Orcish culture means Aggra shouldn't have been left behind on Azeroth during WoD beta. So they put in a plot point where it is discussed.
WoD has been dragging on for so long now that I completely forgot that Garrosh had anything to do with it whatsoever...
"Privilege is invisible to those who have it."
Actually Elements was fine with Killing Garrosh unlike fireballs Elements could not do anything if they do not want to
Just Thrall fell in depression because he Kill Garrosh saying that he feels that is not worthy anymore to weild the Hamer
... you joking? they love that shit. There are half a dozen quests where you use the elements to gain revenge on X or help the elements gain their own revenge on Y.
Elementals are very.. elemental. If you're their buddy, they got you. You want to go cave in the skull of the guy who made you mad? You do you, theyll help. Some of the elementals are even... evil.
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... uh, no. Thrall was using the elements in his FIRST Mak'gora (and the Warcraft Movie has literally nothing to do with the lore of the game, since, you know, it contradicts shit that is set in concrete) with Garrosh before it was interrupted. It's not stated anywhere in canon that you cant use magic. That's fucking absurd.
Thats like telling a mage he has to just use his sword in a duel because you're trying to stack the deck in favor of the warrior. If you want a fair fight, you dont stack one mans weaknesses against another strengths. Its strength vs strength. YOu dont fuck one guy over because he spent his life studying a different path.
Not really. Guldan didn't take control until the end of 6.1
It was the defeat of Kargath and the loss of BRF that caused Guldan to be able to take control.
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I'd like to see a citation that says you cannot use spells. I didn't see that in the rules. Hell the rules even said you can have a shaman bless your weapon.
Also your Guldan Archimonde stuff is completely wrong.
The cipher was only to summon the elemental we killed. That's all. Guldan merely redirected the residual energy of the dark portal we destroyed to open the black gate. You learn this in the very beginning of 6.2 Tanaan when you kill the warlock.