M12S - Mortal Slayer

Upon pulling the Lindwurm, the boss will do a few auto attacks to the two highest enmity players before using The Fixer, which is the generic raidwide of this fight. This raidwide hits for 420k damage by average, which is effectively more than double the max HP your non-tanks have.

There is always more than 90s in between each The Fixer, so make sure that there's at least a MT Reprisal, D1 Feint, Addle, D3 mitigation, a tank 90s and H2 mitigations for every time the boss casts this raidwide. If your party did not get fixer'd, then great! Onto the next mechanic!

Mortal Slayer

The Lindwurm will spawn orbs in sets of two, up to four times, creating 8 orbs in total. These orbs will attack the closest players on the same half of the arena in which the orb is created, in the same order that they were initially created. If an orb cannot find any players on their arena half, then the orb will impact the floor instead, splashing the acid onto everyone and likely causing a wipe.

There are two kind of orbs: green and purple. Purple is considered tankbusters, so these orbs can only be soaked by tanks with heavy mitigations. The pair of orbs can spawn either on one side each or both of them on the same side, but no matter the order, there will always be four on each side at the end of the cast.

Both purple orbs will always be on the same side no matter what, so this will force both tanks to be on one side. To compensate this, the ranged player of that side will swap with the tank in order to make it 4:4 again, providing enough bodies on both sides to soak all orbs. Soaking an orb gives you a vulnerability, so you cannot soak more than one orb.

In order to decide who gets to soak the orbs in which order, we will split up the light parties by having the MT group take care of the west half, while the ST group takes care of the east half. Once split up, the priority will be as follows: Healer > Melee > Ranged > Ranged Flexer.

The tanks have their own priority that overrides the non-tanks, which is the tank who did not swap having a higher priority than the tank who did swap. E.g. if both tanks are on west, its MT > ST and if both tanks are on east, its ST > MT.

Double patterns

This mechanic is simple if the orbs are all spawned 1:1, but there also exists patterns where both orbs are spawned on the same side instead. And within the patterns where both orbs are spawned on the same side, there also exists the very rare pattern where the pair of orbs are 1 green and 1 purple, which requires a specific setup to solve.

In case of a double pattern where theres 1 green and 1 purple, check whether the purple is at the top or at the bottom. If its at the top, then the tank must be closer to the boss than his/her non-tank partner. If its at the bottom instead, then its the opposite.

To resolve a double orb pattern, have one player go in deeper under the boss, while the other player keeps their distance but remains inside the boss's hitbox. There is no agreed rule on how people should preposition, so you can try to communicate through body language or vibe checks to ensure that the pair doesn't PvP each other by accident.

As an additional note, targeted mitigations like Reprisal, Addle, Feint and Dismantle are useless on this mechanic, so save your mitigations for somewhere else instead.

Example 1	Example 2	Example 3