Supremus(Healh -> 3,186,000 ) have following skills :
Enrage—After 15 minutes Supremus will Enrage
Molten Flame—A blue fire trail, originating from Supremus, spreads along the ground towards a random target. The flames do 3325 to 3675 fire damage per second to targets who stand within it. Ability is used every 20 seconds.
Hateful strike—A melee attack which does 27,750 to 32,250 physical damage, before mitigation, to the target with the highest current health within melee range. Its important in this case to have another tank for exemple with higher health than one dps to take impact
Gaze—Fixes aggro on a random target and moves towards the target at 90% reduced speed. Ability has a 10 second cooldown. In test realm i think it is a little bugged in speed, its kinda fast so better be carefull
Molten Punch—Knocks back and does 5,250 physical damage to the target being gazed if the target is within 40 yards of Supremus.
Volcanic Geyser—Randomly summons small volcanoes which deal 4163 to 4837 fire damage per second to targets within 15 yards of the volcano. Very easy to run from volcanos, no more stack in one spot needed.
The boss has 2 phases which it switches between every ~45 seconds.
Phase1; Have your tank with most hp offtanking, he doesn't need to cause threat (the hurtful strike is done on the player with most hp in melee range instead of the 2nd one on threat), have another tank MTing (obviously). Apart from this the raid should dodge the flame paths, there is no random damage going on, so a part from a slow player taking 1 tick from the flame path there is NO healing on the raid needed in this phase, just on the 2 tanks.
Phase2; Very similair to The Darkener (first add at Kael'Thas). Supremus will gaze on someone and follow him around for 10 seconds. He will also do the knockbacks from a few yards for ~5k dmg.
There are a few things which makes this harder though, if he changes gaze and gazes someone relatively far away he will sprint to him untill he's in short range, basically it means you're never 100% safe even if you run very far away.
Also he spawns vulcano's, these are very clear to see and easy to dodge, however, they tick for ~4,5k dmg nearly instantly meaning you will nearly always take a tick.
Still need to check this boss on default realm after update but in beginning we will do this with 3 tanks because when Supremus strikes off-tank for a solid 9-11K, at that point, unless off-tank still has more HP than any of the melee, Supremus can very easily turn around and one-shot one of them. Wit 3 tanks even if one off-tank falls below the melee's HP there is always another one ready to soak Hatefull Strikes.