Summoning Ritual

The Summoning Ritual (50,88) event is completed by killing all the [npc=156652] and then closing the summoning portal. This event is special; after it is completed a number of times (4-5 I think from watching it) a set of three rares will spawn around Neferset at (50,78), (50,88) and (55,79). The possible rares are:

[npc=157472]
[npc=157470]
[npc=157390]
[npc=157476]
[npc=157473] (drops [item=174874]!)
[npc=157469]

You can only close the portal once a day, so you will have to wait for others to complete the event to trigger the rares.

Download the HandyNotes: Visions of N'Zoth addon to see all rare, chest and battle pet locations on your map, filtered by the current assault.

Today we convinced a bunch of characters/players to help with this to attempt to spawn the rare which has a chance to drop [item=174874].

We first got the rares to spawn at 2:28 PM after some unknown number of clicks on the summoning portal.
We finished killing all the 3 spawned rares at about 2:32 PM.

We then repeatedly summoned multiple characters to click the summoning portal one by one following this.
Having clicked the summoning portal every time it spawned on at least 15 different characters, the rares finally spawned again at 3:02 PM.
We finished killing the second set of rares at about 3:05 PM.

Testing then with just a two-player raid group, the summoning portal is able to be repeatedly-clicked by the same player (assuming they have not already received quest credit for clicking the portal).

A 3rd set of rares spawned at 3:44 PM when clicked by a player in a raid group. Yiphrim finally spawned in this set, and all 3 were fully killed around 3:51 PM.

Then at 3:59 PM a 4th set was spawned, again when clicked from a raid group on the 3rd click since the previous set was killed and again with Yiphrim. This was only 8 minutes since the previous set was fully killed. We killed the 4th set of rares sometime after that...

And at 4:07 PM a 5th set of rares was spawned only 8 minutes since the previous spawn, and less than a couple minutes from even killing the previous set.

TL;DR From this research it seems that currently the following may be accurate:

• 
  
• Any click can spawn the rares, even when in a raid group, and without cooldown from a previous rare spawn it's just a low chance or possibly increases with each click? You know, the usual RNG
• 
  
• All previous rares probably need to have been killed Hard to disprove unless they can spawn without killing all prior rares, which has not yet happened
• 
  

So, you want to farm this portal for the Budget toy, and you've unlocked mechagon/nazjatar and have your Heart of Azeroth. However, you are unable to click on the Summoning Portal! If you were like me, you had not fully unlocked the world quests in BFA Uldum yet, despite having WQs in the other BFA zones. To get this, you need to do the "campaign" quests in Uldum from the Visions Of N'zoth questline up to where you unlock the Uldum Accord and are able to see the assault quests on the map. I had stopped at the quest "Titanic Problem" as that was all needed for me to unlock Mechagon/Nazjatar. However as i progressed, I was able to unlock the Uldum WQs and subsequently this World Quest "summoning Ritual" able to begin my farm for the toy via the raid group method. Good luck all and cheers!