Patient Zero

at level 120, soloing the encounter means you'll get this as long as you don't have the debuff when the boss dies.

So to sum this achievement up:

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• Put marker on tank and two markers on [spell=193367]-bouncing people
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• Set marker on the ground for two bouncing people to stack, while rest of the raid avoids that mark at all cost
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• Proceed through Phase 1 normally, as nothing changes there
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• During Phase 2, wait till [npc=114709] casts [spell=193367] on random players
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• Call marked people and [spell=193367] people on ground marker; wait till those two specified people get stacks and remove everyone else from ground mark's location
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• Kill remaining tentacles and MAKE SURE no one else gets close to ground marker
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• In Phase 3, burn Helya to around 20M health
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• MAKE SURE THAT BY THIS POINT DOT PEOPLE STOP DPSING AND PET PEOPLE DISMISS THEIR PETS (affliction warlocks must do both)
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• Stack everyone on marked tank (besides those two)
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• In the right moment (without any annoying Helya mechanics), call [spell=193367] people to stack on marked tank
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• Once stack bounces, burn Helya to the ground as everyone besides one has [spell=193367]
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• If done properly, congratulations on new achievement!
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Soloed this today, very very easy.

- 227ilvl Lock.

Just full set of dots on Helya as Affliction, when Phase 2 started, Grimelord spawned to the LEFT as you face Helya. Instant kill and achievement is yours once boss dies.

Doable at much lower item level for sure.