Thunderfury is one of currently 3 legendary weapons in the game, and is arguebly the best tanking weapon at the moment (due to the high chance of it’s proc). It is no small task aquiring it, and here is how
1. Thunderfury is the reward after a formidable questline. To start this questline you need to loot either the left or right bindings of the windseeker, which drop from Garr and Geddon in Molten Core.
2. Once you loot either binding (the drop rate is very low) take i to Highlord Demetrian in Silithus who sends you onwards.
3. You will now have to gather some items in order to summon Thunderaan. This is no easy task and requires
10 elementium bars
Left and right bindings of the windseeker (ie you need to wait for the other half to drop from either Garr or Baron Geddon)
Essence of the firelord (this one has a 100% droprate from Ragnaros once the quest has started, although only one can be looted on each kill)
Now the challenge here is making those 10 elementium bars. For each bar you need
1 elementium ore (drops from goblins in Blackwing Lair)
10 arcanite bars (requiring 1 arcane crystal and 1 thorium bars each, and each alchemist has a 2 day cooldown on each arcanite bar they create)
3 elemtanl flux (bought from blacksmith vendors)
1 firey core (drops from trash in MC)
Now that is for ONE bar. For the total of ten bars you then need 100 arcane crystals, 100 thorium bars, 10 elementium ores, 30 elemental flux and 10 firey cores, as well as alchemists spending 200 days of cooldown on making you your arcanite bars. It is in other words VERY expensive and time consuming.
In order to smelt all this into the elementium bars you need, your guild must clear BWL up to Ebonroc. After killing the last trash before Ebonroc you are left with Krixix. Have a priest mind control him, and he will teach whoever needs to melt elementium bars. He is hostile, so kill him when the MC wears off.
4. When you got your elementium bars, your essence and both of the bindings, take them to the highlord in Silithus and Thunderaan will be summoned. Bring a raid as you need to defeat him. Loot the Dormant Wind Kissed Blade from him and bring it to the questgiver.
Congratulations, you are now the proud owner of Thunderfury, Blessed Blade of the Windseeker.