Health:

• 10 Man - 8.37M
• 25 Man - 33.5M

Abilities:

Prince Keleseth

• Invocation of Blood - Blood empowers Keleseth, granting him more formidable abilities. He will grow larger when under the effect of this.
• Shadow Lance - Hurls a bolt of dark magic at an enemy, inflicting 17063 to 17937 Shadow damage.
• Tenebrous Shadow Lance - Hurls a bolt of dark magic at an enemy, inflicting 85313 to 89687 Shadow damage. Keleseth casts this when under the effects of Invocation of Blood.
• Shadow Nucleus - Summons a Dark Nucleus. The nearest target resonates with shadow, suffering 1000 damage and reducing Shadow damage taken from all sources by 40% for until cancelled.

Prince Taldaram

• Invocation of Blood - Blood empowers Taldaram, granting him more formidable abilities. He will grow larger when under the effect of this.
• Glittering Sparks - Glittering sparks shoot from the caster's hands in a cone, burning enemies for 16152 Fire damage over 8 sec and reducing their movement speed by 20%
• Conjure Flames - Conjures a ball of flames that flies through the air toward the target and explodes on impact, inflicting 10000 Fire damage to nearby enemies. The ball of flame explodes violently
• Conjure Inferno Flames - Conjures a ball of inferno flames that flies through the air toward the target and explodes on impact, inflicting 10000 Fire damage to nearby enemies. The Inferno Flames discharge some of their stored energy, inflicting 1000 Fire damage to a random nearby target. Taldaram casts this when under the effects of Invocation of Blood

Prince Valanar

• Invocation of Blood -  Blood empowers Valanar, granting him more formidable abilities. He will grow larger when under the effect of this
• Kinetic Bomb - Summons a Kinetic Bomb. The bomb drifts toward the ground and explodes on contact. Direct damage is absorbed by the bomb and converted into energy, propelling the bomb higher in the air with each hit. Explodes on impact with the ground, inflicting 9900 to 12100 Physical damage and knocking enemies back in a wide area
• Shock Vortex - Creates a vortex of swirling force near an enemy target that inflicts damage and knocks back enemies near it. Deals 6000 damage to all enemies within 12 yards and knocks them back
• System Shock Vortex - Creates force vortices on all nearby enemies within 30 yards, inflicting 5000 Physical damage and knocking enemies near the target away. Valanar casts this when under the effects of Invocation of Blood

The Fight:

First off, there's this Orb of the Darkfallen.   Each Prince will only have 1hp and unkillable, unless the Orb goes into him via Invocation of Blood.   This gives them an HP that you can burn down, and is the basis of their "shared hp".   Basically it's the Orb's hp you burn down as it jumps from Prince to Prince to Prince.   Occurs every 45 seconds, random order, though maybe, each one has to be used first before doubling up.   Oh, and they also obtain Empowered abilities during it.

Prince Valanar is the starting prince in the middle and has powers of wind. His first move is Kinetic Bomb, in which a white orb floats slowly to the groud, should it hit the ground, it explodes and knocks people back.   Each direct damage to it though, sends it right back up.  There's 3-4 of these in 25, 2 in 10 mans.   Pets are able to keep one up by itself.   Also must be careful not to overshoot it and hit it above the ceiling for it can pull Blood Queen (if not hotfixed yet).   They also despawn over time, while new ones pop up.   Assign 2ish people to watch over these.

When not empowered, all he does is puts Shock Vortex on the ground which is just a "void zone".  It hurts, and it knocks you back, don't stand in them, they're kind of a wide area swirlying white, well vortex.   

When empowered, the Empowered Shock Vortex, with a 4.5 sec cast, he summons "mini-vortexes" around everyone within 30 yards of him.   Each of them will "explode" doing 5K damage and knocking back everyone within 6 yards.   Treat this like Gruul's Shatter, the raid has to run and spread out so you don't stack up the damage and kill each other.

Taldaram is the prince on the right side and he does fire things.   His first move is a Glittering Fire Sparks, which is a random target frontal cone aoe.    One of those like Slime Sprays where he just turns and fires.   It is likely the raid won't really notice this unless they're on him at the time.   Anyways, heal through it, mass dispel it, etc.

When not empowered, he fires a Flame Orb and some random raid member.   It's similar to Putricide's Gas Cloud in that there'll be 15 stacks, decreasing with time, and will explode if it reaches its target, damage based on stacks.  So the target is to simply kite it around until the stacks drain off.

When empowered, the Empowered Flame Orb, changes its mechanics slightly.   The only way to drain the stacks is to stand (walk/run) under it and let it shoot people with fire beams.   The more it hits the more stacks it loses.   So the goal there is while kited, the raid is to run with it, along the kite path soaking the hits.

Keleseth is the left one and does shadow damage.  Typically, a ranged tank is used for him.  His only real trick is the he fires Shadow Lances, just shadowbolts.   Continuously.

Except he also spawns Shadow Nucleus around the room, or maybe around people.   What those do is latch on to the last person that hits them and gives them a 1K dot, and 35% reduction in shadow damage taken.   You ranged tank will want these and will spend almost the entire fight collecting them.   If needed, other people can collect them too and bring them to the tank, for he can just pull them off for himself.  They also despawn over time so yes, collect the whole fight.   You'll need 3+ to survive...

When empowered, his Shadow Lances start hitting for 80K.   So your ranged tank will need those Shadow Nucleus to survive.   External CDs may also be needed.  Also as a note, remember they latch onto the last person that hits them, so your dps should not aoe anywhere near your ranged tank.    You could wind up pulling some off leaving him vulnerable to an insta-gib

That's about all to the fight.  It's a fairly easy fight, after the raid learns and sees what each individual ability does and reacts appropriately to them..