Basic Mechanics
At the start of the fight, Tequatl lands, summons minions and poison puddles, and immediately starts building a Hardened Scales buff. This buff causes a Bone Wall to spawn at 20 stacks, which makes the boss immune to damage while it’s up. Since you only have 15 minutes to kill the boss any bone walls summoned will waste time and cause you to fail, so it is critical to keep the boss from reaching 20 stacks. UPDATE: This mechanic does NOT decrease damage taken by Tequatl, it does nothing until 20 stacks when it summons a Bone Wall. Source: ANet
6 Hylek Turrets surround the boss, which have 4 skills that are important.
Turret Skill 2: This skill removes a stack of the Hardened Scales buff and must be used on cooldown. Use the ingame targeting function (you no longer need a party to do this) to make it easier to target Tequatl and fire skill 2. If all turret users fire skill 2 on cooldown, Tequatl will have <2 stacks of his buff up at any given time. You know the turret teams are not doing their jobs if Tequatl begins to build stacks higher than 5 or even 10.
Turret Skill 3: This skill removes poison puddles and has two major uses. It should be cast on the zerg to remove damage to them, and whenever a poison puddle appears at the base of a turret it should be fired on itself to prevent the turret from breaking. If the turret does break it can be quickly repaired with the nearby repair hammers.
Turret Skills 4 & 5: These skills give a lot of boons in AOE range to the targets. It is best used either on the turret defenders or on the Zerg if they are close enough together, and on cooldown while waiting for Skill 2 to come up.
Strategy
Groups: There should be three major groups of players—Turret Users, Turret Defenders, and The Zerg.
Turret Users: There are only six turrets so only six players can be the Turret Users. These six players are the most important participants in the fight, so only people who know what they are doing should use the turrets. If even one Turret User does his or her job incorrectly the entire event will fail.
Turret Defenders: The Turret Defenders should likely be composed of squishier classes that have trouble surviving closer to Tequatl. They should be safer defending the turrets and be more helpful to the server instead of dying constantly in the front lines with The Zerg. My server is playing around with creating small parties of 3-5 Turret Defenders per turret, for a total of 18-30 players defending the turrets.
The Zerg: Everyone who isn’t a Turret User or Turret Defender is part of the Zerg. These players need to stay as close together as possible to benefit as much as possible from the turret skills 3, 4, & 5. If the entire Zerg can be coordinated enough to remain stacked near each other then the Turret Users only need to fire skill 3 at one spot, preventing the poison damage to everyone. If the Zerg spreads out too much the Turret Users will be totally unable to buff them or remove poison from everyone, and people will die. If you are part of the Zerg find a nearby commander and stay stacked near them. Move slightly to get out of poison circles, but otherwise STAY TOGETHER!
If anyone has any other thoughts/bullets to add please comment!
UPDATES
#1: Updated to reflect the post from ArenaNet indicating that the Scales buff does NOT reduce damage taken, and does nothing until it summons a bone wall at 20 stacks.
#2: Upon attempting the fight again our server learned a few things. One, the 1 skill on the turrets does a lot of damage to Tequatl, but only if you target his head. It does about 2400 damage per shot to his head. You should use skill 1 whenever your other skills are on Cooldown. Two, the Elixir skill (4) gives Quickness and is like firing a targeted Time Warp. If you cast it on yourself you can hit two turrets and get quickness when firing the 1 skill. This seems to be a good way to quickly damage Tequatl.
#3: We’ve become aware of a BUG that will impede your progress. When you are using the turrets, occasionally your skills will activate and go on cooldown, but have no effect. You can tell this has happened if the skill goes on cooldown but you see no harpoon animation (skills 1 & 2). To fix the issue get off the turret and then get back on it. I’m sure this isn’t helping servers if folks are sitting on broken turrets for the entire fight!
(edited by Lithril Ashwalker.6230)