Took the Red Eye Down

Easy Solo for Level 120 Battle for Azeroth and Beyond...

1. Normal Difficulty.

2. Begin Fight. Minimal opening damage to Il'gynoth.

3. Basically just kill tentacles until 20 Nightmare Ichors have spawned. Do not attack the Nightmare Ichors.

4. It'll take a few minutes so just run around and easily kite them, until you feel you've collected 20, I was overly careful and had 27 by the time I was comfortable enough.

5. Once you have your twenty, move right into the eye and use your classes AoE attack to wipe out all the Nightmare Ichors simultaneously.

6. Their explosion and your aoe damage combined should begin the next phase.

7. Walk in and kill the boss.

8. ?

9. Profit. Achievement Completed.

This is a fairly easy one to solo as of patch 8.0.1, I just managed it as a level 120 ilvl 300 Blood DK. Waited until I had 24 following me just in case and the blasted them with Blood Boil in front of the eye.

Here is a macro I used to count the number of Nightmare Ichor currently on screen which helped a great deal!

/run local t,c="Nightmare Ichor",0 for i=1,10000 do local p=C_NamePlate.GetNamePlateForUnit("nameplate"..i) if p and p:IsVisible() and p:GetChildren():GetRegions():GetText()==t then c=c+1 end end print(t,":",c)

Dominator Tentacles spawn 4
Deathglare Tentacles spawn 2
Nightmare Horror spawns 4
Corruptor Tentacles spawn 1

The spawn order for the first phase is:

Dominator (x2), Deathglare (x1), Nightmare Horror (x1), Corruptor (x2), Deathglare (x2) = 20

While the achievement doesn't track, 20 ichors is the number needed to kill the eyeball, so if you only aim for the above, you should have a very good idea whether or not you've succeeded.