Two phase fight. In P1 you fight 2 Elementals with different abilities. When one drops to 50% HP, they merge and P2 starts.
In P1, on Normal, tank the 2 Elementals together. Bring them both to 50% HP at the same time to shorten P2.
In Pi, if you're within 50yd of an Elemental, you gain stacks of its DoT. On Normal the raid will stack both DoTs but P2 should start before it becomes dangerous.
When either Elementals drops to 50% HP, they merge and P2 starts. The new Elemental combines their remaining HP and abilities.
If the 2 Elementals are not at least 25yd apart, they deal 200% more damage. Keep them separated.
Casters can stand between them to cleave but would stack both DoTs, so make sure your healers can handle it. If not, simply play the swap. Melees should start on Fire Elemental and swap if needed.
In P2, the Shadowflame Amalgamation gains a mix of the previous abilities. You must soak some projectiles AND dodge others.
You fight the Elemental of Shadow and of Fire at the same time.
Raid damage taken ramps up. Bring them both to 50% HP at the same time.
TANK BOTH ELEMENTALS APART.
CASTERS BETWEEN BOTH ELEMENTALS.
MELEE START ON FIRE ELEMENTAL.
Players within 50yd of the Fire Elemental stack a 20s Fire DoT.
Players within 50yd of the Shadow Elemental stack a 20s Shadow DoT that reduces their max HP.
Casters can stay between both Elementals stack both DoTs and take heavy damage. It's a riskier strategy.
Melee start on Fire Elemental and swap to the other if needed.
Shadow Elemental Abilities
DODGE THE ORBS.
MOVE AWAY FROM
THE DETONATION POINT.
Fire Elemental Abilities
SOAK THE FIREBALLS.
SOAK THE METEORE.
When either Elemental drops to 50% HP,
they become immune and merge into
a new Shadowflame Elemental.
BRING BOTH ELEMENTALS TO
50% HP AT THE SAME TIME. DODGE
THE PUDDLES WHILE THEY MERGE.
The new Shadowflame Elemental combines their remaining HP and abilities.
SOAK PROJECTILES AND
DODGE THE ORBS.
THEN MOVE OUT.
MOVE OUT WITH
CIRCLES AND DODGE
DODGE THE CONE.
A general WeakAura pack that provides "icon" style mechanics/debuff as well as short descriptions for each. Pretty standard. We also recommend downloading Causese Sound addon to hear vocal announcements. Feel free to thank the amazing Causese here (sorry, no Twitter that I know of...).
Another must have by Causese if you play or are planning to play tank. It informs you when to taunt and how your co-tank is doing with their mechanics.
Make sure to checkout the Causese Sound addon to also pair it with appropriate sound announcements.