Tank: Adds spawn according to his health, and faster the harder he is pushed. Chain them into the group. A large Flesh Atronach joins at low health; hold it.
Dps: Use area damage on the adds, and interrupt or kill the healer adds first if damage is low. Block the Flesh Atronach's heavy attack if it targets you.
All: A large stationary circle appears beneath a random player. Step out of it.
All: A large heavy attack with knockback. Block it if it is on you, in any role. If it is aimed at a DPS or healer, the tank has lost aggro.
All: A clearly telegraphed heavy attack on the aggro holder. Block it; if she turns on a DPS or healer, they block until the tank recovers aggro.
All: She casts lightning at the group. Stay together so the healer can cover everyone.
Tank: Bring the incoming spiders into the group for area damage rather than letting them spread.
Dps: Keep area damage on the spiders while damaging the boss.
All: She cocoons a random player, who cannot free themselves. Another player moves to them and activates the synergy immediately. Staying stacked makes this quick.
All: A very hard-hitting heavy attack. Block it whenever it is incoming, in any role. It kills a DPS or healer if the boss is not controlled.
Tank: It has a dangerous frontal attack. Keep it facing away, with DPS and healers behind, not beside, the tank.
All: It creates a damaging effect around itself. Watch the ground and step out.
All: Block the heavy attack if it is on you. The tank keeps it facing away. Otherwise this boss is simply a very large health pool.
All: A large, clearly visible ground effect. Move out of it rather than trying to heal through it.
All: Block the heavy attack; it should be on the tank. If she turns on you, block until the tank recovers aggro.
All: She teleports the group out and scatters them, each with a large circle around them. These must not overlap; overlapping circles are lethal. Do not move back toward the boss or another player until your circle is clear of everyone else's and the mechanic ends. Spread out around her before it happens.
Hard Mode: There is no scroll. Hard Mode is a condition on the fight: keep four of Nerien'eth's ghosts alive until he takes the Ebony Blade at 35% health, then kill them all (achievement: The Blade's Edge). See the Ghosts (Hard Mode) callout.
All: He spawns crystals around the room; a chain rises and then a burst erupts. It is easy to see; step out of each effect.
All: He channels and fires a skull projectile at a random player, looking directly at the target. Dodge-roll as it reaches you; a miss deals very high damage and a knockdown, and can be instantly lethal. Spread out slightly so everyone can see who is targeted.
All: He teleports onto a random player, then a large spreading effect erupts from his feet. The instant he vanishes, move well away; one dodge may not be enough.
Tank: Each time he teleports to the ghost figures he releases two ghosts. On Normal, hold them and let the group kill them before the next pair.
Dps: On Normal, kill each pair of ghosts before the next arrives, or you are overwhelmed.
All: At 35% health he takes the central sword and stuns the whole group, then holds a random player in the air and drains them. The target activates the synergy to resist; everyone else breaks his damage shield to release them. Afterward he fights with the sword: heavy melee and random charge attacks (block if aimed at you). He may repeat the drain behind another shield.
All: On Hard Mode, do not kill the ghosts: the tank pulls them aside and the group avoids damaging them. Four ghosts must be alive when Nerien'eth reaches 35% health, so hold back boss damage if needed to avoid pushing past that point early. Kill the ghosts only once he takes the sword.