Falkreath Hold

Basilisk Powder

All: A poison cone thrown in front of her that stuns and then deals poison damage over time. Stay out of it.

Catapult

All: She calls siege fire onto the group. When she raises a shield, get inside it to avoid all the incoming catapult shots.

Health Potion

Dps: She drinks a potion to heal. Interrupt it to stagger her instead.

Ground effect

All: Small harmful circles appear underfoot periodically. Step away from them.

Charge

Tank: A long charge with a ground effect that knocks down anyone in its path. Position the mammoth with its back to a wall so it cannot get a clean charge lane, and block it.

Sweeping Tusks

Tank: A charged heavy attack. Block or dodge it. Nobody but the tank stands in front.

Minion Flame effects

All: Reachmen on the mountains above cast moving ground-fire effects. Weave between them; do not stack.

Stomp

All: Past roughly 50% health the Reachmen set the mammoth on fire and it adds a rearing stomp for very heavy flame damage around itself. Everyone blocks the instant it happens, without exception.

Erbogar, Mochveda and Tuecille

Dps: Three necromancers must die before Cernunnon appears. Interrupt their channels: Erbogar's arrow splits into four flame effects, Tuecille's Death's Herald knocks back, and both drop root effects. Kill the mage first, then stack the melee onto the archer.

Carry to the Graves

All: A defeated necromancer kneels instead of dying, glowing. Pick them up and carry them to one of the three lit graves around the arena. Leave one too long and it heals back up and rejoins the fight.

Clash of Bones

Tank: A charged heavy attack with a knockback. Block it, or dodge if you are not tanking.

Aspect of Winter

All: A rune appears under a player, then a meteor lands there for heavy frost damage. Move away from the rest of the group before it lands and hold block. Overlapping meteors from multiple players is what actually kills people here.

Brush with Death

All: Wraiths roam the arena and fear anyone they touch, and summon Ravenous Revenants. Avoid the wraiths; kill the revenants.

Pull of the Underworld

All: A soulstorm barrier surrounds the arena the moment you enter. Stay inside the eye of it, or take heavy ongoing magic damage.

Summon Minions (about 50%)

Dps: At roughly 50% health he vanishes and resurrects all three necromancers. Repeat the interrupt-and-carry cycle before he returns and the fight continues. There are no new mechanics the second time.

Fiery Breath

Tank: A frontal fire cone. Block it, and keep him faced away from the group.

Lava Whip

Tank: A charged heavy melee attack. Block it.

Dark Talons

All: He roots everyone around him and deals fire damage over time. Dodge roll to break free.

Summon Draugr

Tank: Weak draugr spawn throughout. They die easily, but their corpses matter for the next mechanic, so pull them somewhere central rather than letting them scatter.

Dps: Kill the draugr quickly. Leftover corpses feed Deathlord's Fury.

Deathlord's Fury

Healer: He channels a spell that fires magic bolts from every uncleansed draugr corpse in the arena. Damage scales with the corpse count and cannot be avoided, only reduced by cleansing.

Dps: Grab the purifying buff from the urns in the corners of the room and cleanse draugr corpses before he casts this. With no corpses up, the attack does nothing.

Fiery Blast

All: A charged ranged heavy attack for very heavy damage. Block or dodge it.

Ring of Fire

All: Flames ignite along the hall behind the pillars; group up and stack closely inside the centre of the arena.

Pillar Eruption / Pillars of Nirn

All: While Ring of Fire is up he pulls and snares everyone, then nirncrux pillars erupt underfoot and linger, dealing fire damage over time. Keep moving and do not let your pillar overlap anyone else's.

Pyroclasm

All: Flames burst continuously around him in the center; clear out to the perimeter edges behind the pillars.

Stoke the Embers

All: He pounds the ground and fireballs travel outward along it. If the outer edge is currently safe, hide behind a pillar to avoid them.

Master of the Elements

Dps: At 80%, 60%, 40% and 20% health he becomes invulnerable and summons a Flame, Frost, Stone and Storm Atronach. Kill them quickly, before he wakes and you are fighting both adds and boss at once. The invulnerable window shortens each time, so later waves are tighter.

Grovel / Shout of Desolation

All: At 70%, 50%, 30%, 10%, and 5% health he shouts for massive unmitigable damage, lethal on Veteran. Because any pillar with a player behind it shatters when the shout lands, the entire group must coordinate and run to the exact same pillar for every phase to preserve the arena layout.

Elemental Totems

All: The four totems around the room (Flame, Frost, Shock, Stone) periodically fire an elemental bolt at a random player for moderate damage. Watch for the tell.

Damage Shield (Hard Mode execute)

All: Below 20% health he alternates Shout of Desolation and add waves on a timer. Finish him before you run out of pillars, since the next shout with none standing wipes the group. On Hard Mode he also gains a damage shield in this phase; save ultimates for the execute to break it and finish him before the incoming damage becomes unsurvivable.