This fight is actually rather complex, especially for the second boss of a tier. You simply will not be able to kill this boss without almost every member of the raid sticking to a detailed plan.
The main goal of this fight is to move your raid and MOTHER through two barriers (item), so that she starts taking double damage and can be nuked down. The idea is simple, but several factors complicate the process. When any player crosses the barrier, it does significant damage to the entire raid and spawns an add on that side of the barrier that needs to be interrupted and killed. Also, the barrier effectively prevents any casts going through it, so you can only damage or heal what is on your side. As a result, this fight ultimately boils down to sending the right players though the barrier at the right times. There are other mechanics in the fight that will be mentioned below, but they don’t have as much impact on the strategy.
This fight is mostly single target if you’re assigned to cross the barrier late, and mostly stacked cleave if you’re assigned to cross early. We recommend using Bloodlust once the boss and all dps have crossed the second barrier, as this is where she takes double damage and can be focused down. She forfeits at 10% health remaining.
Before you pull the boss, designate which tank takes the boss and which tank handles the adds. Also determine the order your dps and healers will pass through the barrier. About 5 seconds after pulling the boss, send the add tank, a healer, and a good cleave dps with an interrupt through the barrier all at the same time. After that, send your dps through one at a time, making sure the raid is healthy before each one. Also send a healer through for every 3-4 dps. The last players to go through should be the boss tank and the final healer.
Keep the boss faced away from the raid as much as possible. She occasionally does a frontal cone cast in the direction she’s facing, which can be dodged by the tank as well (item).
Make sure every cast of every add is interrupted (item). The adds can be stunned, gripped, knocked back, etc.
Once the boss passes through the first barrier, two different patterns of quickly moving laser beams appear frequently for the rest of the fight (item). The vertical lasers come from either side of the room and leave a safe gap you have to stand in as they pass through. The horizontal lasers come from the ceiling and mark a safe gap on the floor before they come down. The lasers move fast and essentially one-shot you, so everyone needs to react to them quickly and get to the safe gap as soon as possible.
Repeat the exact same process for the second barrier. Once everyone is past the second barrier, Bloodlust and nuke the boss until she forfeits at 10% health.
Don’t be in front of the boss.
Dodge fire swirlies. Run against wind. Stand in safe gap of laser beams.
Run through the blue barrier when told. Kill and interrupt adds after you pass through.
Any and all raid-movement speed increases are incredibly useful in this fight. Running against the wind and dodging lasers can involve long stretches of movement, and extra speed could actually save a wipe.
Almost all of the damage taken in this fight is avoidable. The only other damage going out is melee swings on tanks and Defense Grid pulses.
The more geared your group is, the faster you’ll be able to send people through the barrier. The Defense Grid won’t hurt as much, and healers will be able to keep up better.
The only thing tanks specifically have to worry about on this fight is the Sanitizing Strike from the boss. The boss just needs to be faced away from the group as much as possible, and the tank just needs to side-step it during the 3 second cast.
Healing the pulses from Defense Grid is going to be the main focus for healers. The faster the group recovers from these pulses, the faster you can send people through. If you really want to optimize how fast you get through the barriers, assigning healing cooldowns would allow you to send huge packs of players through at those times.