Well Vaelastrasz the Corrupt is the boss that killed 60 guilds. It was incredibly difficult back in the day(so i hear).
There are a lot of mechanics to this boss fights, but overall it's very simple.
1. Every 45 seconds, a tank will die. Essence of the Red lasts 3 minutes, so that's 4 Tanks. I am guessing we might need a 5th tank. More like an emergency tank in case something bad happens. But at least 4 tanks. As long as the tanks can correctly swap when the others, it'll be fine.
2. Melee DPS need to be kept 10 yards away from the tanks, while the tanks are facing the vael away from the raid. That way they are not risking getting hit by the cleave. A lot of the AoE abilities can be avoided as long as the tanks position the boss correctly.
3. As long as anyone with BA moves out of the group, we'll all be fine.
4. We'll need a total of 12-13 healers(for a full 40man group). 1 Healer for every group, and 1 healer for every tank. If one of the Group healers dies from BA, one of the tank healers will take over for that group and heal them while offhealing the tank if needed.
5. Everyone will be given a
Greater Fire Protection Potion. Since we do not have fire resistance available, this is the best we can do. We will probably use this when our group healers die. Or for whatever reason, you get incredibly low; this will be your emergency heal.
6. Positioning is the key. As long as everyone does their job and stands where they need to, we'll be fine. It's a DPS race. You either kill him before 3:00, or you wipe 15 seconds after. This is going to be a huge test to our healers because we will need to constantly be healing nonstop during this fight.
Heal through Fire Nova and keep the current tank alive during Flame Breathe for 45 seconds. Make sure His Flame breathe and cleave dont hit the raid. Tank Swap correctly. Move out of the groups during Burning Adrenaline. Stay away from his tail. Stand in the correct Position. And DPS the boss down within 3 minutes.
This boss is very possible to down at fifty. The real question is going to be what's the minimum amount of people needed for the fight. We don't know if we can do this with 25 people, 30 people, or if we will need a full 40man and just barely make it with just that.
And the next two bosses after him dont get any easier from my PoV, BWL is mouthwatering haha