Servant of N'Zoth

Eridana-ZJ's Guide to getting N'lyeth, Sliver of N'zoth

A couple of things I’ve noticed and how I got this achievement done:

Shortly after you kill one or two of your own faction, there is a high probability that you will become bounty hunted. This makes killing people of your own faction difficult since you can’t fly and the opposite faction is chasing you down.

I was bouncing around Nazjatar trying to get it done, but would get overrun when the bounty on me happened.
I tried logging out for a bit to see if bounty would drop, it dropped the bounty, kept assassin, and dropped my quest.
Hearthing or teleporting to other BFA zones seems to also drop the quest.

Wouldn’t it be great if you could kill some of your faction and hide from the prying eyes of bounty hunters? You can!
But I recommend gathering some sacrifices, I mean a few friends, to help. 
If you get 4 sacri-, er, friends, you can be done in 21 minutes after accepting your tentacles from N'Zoth.

This is a great week to get the toy because of Call to Arms: Nazjatar. 
Why? 
Mardivh’s Lab is why. :-D

This place has been a favorite spot to hide while trolling. It’s also a perfect spot to hang out and bathe in your tentacly glory while you’re a bounty.

So. While you’re waiting here, invite 4 friends over to the mouth of the cave. I was able to invite them to group to make sure they were in the same shard as of today. Once they are there, have them take off all their gear, pop out of the cave for a few seconds, mow them all down with focusing iris, and make your way back to the safety of Mardivh’s lab.

Your buddies will have a 10 minute debuff not allowing their deaths to count towards your progress. They can put their gear back on and fly off to do other stuff and come back in 10 minutes for more laser to the face. Some will try to find you in the cave, but it’s been my experience that people chasing your bounty will just fly away, because they realize you’re trolling them in the cave. When your buddies come back, have them tell you when the coast is clear and mow them down again.

Repeat the process three times and you're done. This should take a little over 20 minutes after you use the sliver. Make sure you're at 100% HP before using it! 
Join me and fight for N’Zoth! <3

UPDATE: I've been reading other comments that say their quest item kills them. This leads me to believe that the Sliver of N'Zoth's damage effect can CRIT!
I noticed it hurting more than it should while trying to do the quest and didn't really put much thought into it. Sometimes it would chunk me down to about 15-20% health, but would never kill me. Even now that I have the toy it will chunk me every once in a while.

The only reason I think I have been surviving every time it crits is because my WPVP set has ~12% versatility. I highly suggest using a defensive or having a decent amount of versatility when you use the quest item/toy. Keep in mind that it is shadow damage.

Has a chance to instantly kill you. It says it deals 60% of your hp but sometimes it instantly kills you, making you fail the quest and requiring you to get assassin again to get it. (and waiting for the 1hr cooldown to go away)

Got the quest, used the item, my character instantly died. Failed the quest