The 4th boss encounter of Lair of Maarselok is "Maarselok on his Perch"; it's the one where you have to prevent hoarvors from reaching Selene and protect the Shagrath's Hosts (green spiders) from the strangler spawns.


How does the spider mechanic actually work?

Every 3 seconds, Selene will summon a new Shagrath's Host (green spider).

Each time a spider climbs all the way up to Maarselok, it gives Maarselok a stack of a debuff named "Spider at Top". This debuff lasts for 10 seconds and is refreshed each time the boss gains a stack. When the boss has gained 5 stacks of the debuff, he is grounded and can be damaged.

If 10s go by without any spiders reaching the boss, the debuff expires and the stacks are reset to zero.

So how do you end up with a 10s gap in the chain of spiders? Well, if you let a hoarvor get to Selene, it will stun her with an effect aptly named "Boom" that lasts for 7 seconds and no new spiders will spawn during that time.

And of course, stranglers can kill spiders. And therein lies in the rub. The stranglers' spit will immediately kill any spider that it targets because it's a 1-shot against the spiders.


What is wrong with this mechanic? Part 1: Shagrath's Shield

I had never bothered to look at this mechanic in detail until we tried to get the Shagrath's Shield achievement, the last achievement from this dungeon that we're missing. At the moment, I feel that this achievement is impossible unless we get incredibly lucky.

Why? Because the stranglers' targeting appears to be random. Sometimes it'll target a player. Sometimes it'll target a spider. And if it targets a spider, that achievement is gone.

No, doing damage to the stranglers do not make them target you instead of the spider. Here is a clip showing all three DDs hitting the strangler, and the strangler ignoring us, spitting, and killing a spider.

Yes, we tried having DDs slot taunt and taunting the stranglers. No, their spit is still random and does not respect taunt.

Yes, the stranglers can be CC'ed. But with the incredibly high rate of strangler spawns, all it takes is for one strangler to spawn and spit at at a spider before the CC could be placed to lose the achievement. And CC durations are too short--typically on the order of 2s or so--and that's not enough time to burst through 172K health.

With the help of an addon custom-made just for tracking this achievement, I can see exactly how many and when a spider dies. And, ultimately, it comes down to luck. We've had a few lucky phases where no spiders died because the stranglers targeted us. But we've never had three lucky phases in a row.

Again, all it takes is for one strangler to spawn, randomly pick a spider as a target, shoot a single spit, and the achievement is RIP. And all this could happen before players could reasonably react.


What is wrong with this mechanic? Part 2: Inconsistent Groundings

This is something that I've heard from a lot of groups. That the times to ground Maarselok can be inconsistent. Most of the time, he grounds fairly quickly. But sometimes, it seems to drag on forever. We saw this for ourselves during our first clear of this boss on Live. Our first and third phases/groundings were very quick. And the second phase/grounding took 6 times as long.

Now that I understand the mechanic better and know what to look for in the logs, the problem becomes pretty clear. We had incredibly bad luck on that second grounding, where it seemed as if the stranglers had a much greater affinity for the spiders than players. There were three times when we built up 4 stacks on the boss only to lose it due to the unusually high number of spider deaths. We also had one hoarvor stun which exacerbated matters, but that had happened after we had already lost a 4-stack due to spider deaths.


What can be done?

Option 1: Make the stranglers more manageable

Personally, I think the random nature of the strangler spit is one of the biggest problems. If a strangler is being damaged by a player, it should target that player and not target a spider.

The other problem is that a strangler, upon spawning, could choose to immediately target a spider for spit. There isn't a reasonable amount of time for players to react. Adding an initial cooldown to when they could spit at a spider would help.

Option 2: Make spider deaths more forgiving

Relaxing the requirements on the achievement (i.e., changing it from "0 dead spiders" to "no more than X dead spiders") is probably the most direct fix for the achievement problem. Increasing the 10s reset time would help with the inconsistency problem.

@ZOS_Finn