Let Me Solo Him: Nullaeus

Tank specs like Brewmaster Monk (ilvl 244+) and Guardian Druid (ilvl 256+) can survive Nullaeus, but switching to a healer spec and letting Valeera deal damage as DPS is significantly easier — Guardian Druid healers have finished the fight with minimal effort, with Valeera dealing the bulk of the damage while you keep her alive with Lifebloom and Rejuvenation.

Set Valeera to DPS if you are playing a healer spec, or to Healer if you are playing a tank or damage spec; recommended curios include the Overflowing Voidspire paired with either the Nether Entropic Kris or the Porcelain Blade Tip depending on your setup.

Nullaeus casts Emptiness of the Void, which is a one-shot ability — interrupt it every time it is cast and do not interrupt his other spells; Shadow Priests can use Silence on its 30-second cooldown to cover every cast.

Nullaeus summons three waves of adds at approximately 70%, 50%, and 25% health — the first two waves contain mobs that apply debuffs, so save cooldowns and kill them quickly; the final wave is a single caster mob that tank specs can ignore and rush the boss through, while healer Valeera will automatically dispel the Devouring Essence debuff from you throughout the fight.

Nullaeus briefly loses Valeera as his target for about half a second each time she vanishes as part of her rotation — avoid healing Valeera during that exact window to prevent pulling aggro off her; keeping Nullaeus as your focus target makes it easier to track who he is targeting.