Gruul:
HKM Fight:
1 tank (Paladin / Warrior / Bear) HKM
1 tank (P/W/B) The Priest guy
2 tanks (Hunters / P/W/B) The Shaman, or 1 druid (no polymorph)
1 tank (mage) The mage
0/1/2 tanks + lock (P/W/B, can be pet tanked by enslaved) The warlock.
Gruul Fight:
1 MT (P/W/B) Gruul
1 OT (P/B, W as 3rd choice) Hurtful strikes
1 3rd tank (P/B, W/3rd) when one of the above dies
HKM is messy, essentially you need 1 tank on HKM, 1 tank on the priest and 1 on the lock (easier with 2), the shaman can be hunter tanked (or any class really, you spend most of the fight polymorphed

), and the mage really needs a mage to tank him, you can do it with other classes, its just less fun
Gruul is easy, you really want 2 tanks (1 to tank, 1 to eat bolts and save your melee dps/ MT from getting squishified). A third tank is often useful here. By preference I would put a bear of paladin in the 2nd and 3rd slots as their threat is much better as OT I have found (remember the 2nd/3rd tank needs to be 2nd on the aggro list if the MT dies or someone squishier bites it). The MT slot is open, probably pref to a warrior but paladins and bears can do it with relative easy. One thing to note is that if you have a 3rd tank / the raid it should not distract healing from the MT and OT. Gruul can hurt lots (15K crushes @ growth 15 I have eaten when I got silenced with HS nearly out of cooldown, 2 of those put me down

)
Magtheridon:
Channelers:
By preference 4 tanks, preferably 1 paladin / bear for the first 2 and tank them as a pair. The tank on these ones will likely pick up Magtheridon (your 2nd tank could also do so but you may not have that channeler down). Preference to 5 locks, but any number of locks + some hunters or similar can do the cc for the infernals.
Magtheridon:
Warrior or Paladin by preference, Bears can do it but crushes can be very painful. Paladin threat is essentially limitless on this fight, if you oom you are doing it wrong, and Maggie is a demon

.
We typically take 3 Tanks to HKM/Gruul, at least 2 hunters and some locks (pet tank ftw

), the third tank on Gruul just fights to stay 3rd for the case when the MT or OT die (surprisingly not rare, healers seem to forget about the tank a lot in this fight).
Magtheridon we typically use 4 tanks + 4 locks / 2 hunters as the tank / cc contingent with the first tank on 2 mobs taking up Magtheridon when he breaks. Our tanks basically go: Maggie tank, weakest -> strongest as the channelers increase damage a lot (though tbh we are running out of stuff to differentiate warrior tanks by since the gear is equalising a lot). Typically I tank Magtheridon because I have the highest hits, and I can tank 2 channelers with easy meaning the dps can nuke straight off, by the time the dps hit the 3rd channeler there is no way they can pull, and I get to do big threat on Magtheridon.
TK so far we take 4 tanks, 2 warriors, 1 any (bear?) and 1 pally if we can. The warriors make the sentinels a much easier fight (not saying you can't tank them as a bear / paladin, but warriors have it easy). Bear typically goes dps on VR.
SSC 4 tanks, typically 2 warriors 1 random and me / another warrior.
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