Please note that this list is not necessarily comprehensive, as I do not have the means to test some of the more advanced bosses (such as those in Antorus, or mythic difficulty from Trial of Valor and beyond). These assessments are based solely on mechanics… Many other bosses are currently unsoloable but will likely fall to the next tier or two of raid gear. For a list of bosses that I’ve proven ARE soloable, I have a list here.

Emerald Nightmare

  • Dragons of Nightmare (Mythic): currently unsoloable due to a Mythic-only mechanic. At 90%, 60%, and 30% health, a Lumbering Mindgorger add will spawn inside one of the portals around the edge of the arena. If they are not killed before they reach full energy, they will wipe the raid via the Devour Nightmare ability. The problem is that entering a portal while soloing doesn’t work: it kicks you back out immediately. Thus, you WILL die not long after the first Mindgorger spawns.

Trial of Valor

  • Odyn (all difficulties): I hate you, Valarjar’s Bond. I suppose you can solo this, with some difficulty, as a pet class, but everyone else is 100% out of luck until this ability is nerfed or removed. EDIT: I’ve found a way to solo this! Check out my strategy here.

Nighthold

  • Krosus (all difficulties): the problem here is Searing Brand, a stacking DoT that is applied every two seconds until you’re dead. It’s meant to force frequent tank swaps, but since you’re soloing, it forces frequent repair bills.
  • Star Augur Etraeus (all difficulties): Absolute Zero is the cause of all the pain here. It’s a heavy, stacking DoT with infinite duration that can only be removed by at least 3 other players. Thus, it’s a death sentence for soloing. I’ve yet to make it past phase 1 due to this mechanic.

Tomb of Sargeras

  • The Desolate Host (all difficulties): since you’re soloing, you can only fight in one realm (corporeal or spirit) at any given moment. This means that you will constantly trigger the Quietus ability, which is stacking shadow damage. It will kill you LONG before you kill the boss.
  • Mistress Sassz’ine (all difficulties): I’m not 100% convinced that she’s unsoloable, but it certainly seems that way. The problem emerges in phase two, when Sassz’ine summons Sarukel and his Devouring Maw. The intended way to deal with this is to pick up Befouling Ink and bring it to Sarukel three times, forcing him to leave. Unfortunately, Devouring Maw seems to have an undocumented “berserk” timer, after which the pull becomes impossible to outrun, causing instant death. This is compounded by the fact that, since you’re soloing, only one pool of Ink will form at a time, and the Devouring Maw insta-kill kicks in after only two have dropped.

Antorus

  • Antoran High Command (all difficulties): pure speculation on my part, but I suspect that the fight will reset if you attempt to enter one of the control pods, rendering the fight impossible to beat.