From Darkness Comes Light
The strategy for this boss is the same as the previous 10man versions that I have done so I wont go too much into strategy here. See link below for the 10man version.
For the 25man version, for those who have been trying, one issue you'll immediately notice is that Sara doesn't always stop casting Psychosis once you reach below 40 sanity. Sometimes she doesn't stop until you reach 28, 16, 4 or even 0 sanity. As a result almost half of the attempts were wasted because she didn't stop casting Psychosis until I went insane.
Sometimes when she stopped on 4 sanity, I thought to play it safe by standing in sanity restoration well to gain just 1 tick of sanity back (20 sanity per tick). But that 1 tick takes seemingly forever, and as soon as that one tick comes, it seems hard to move out of the well in time before the 2nd tick comes, which then ended up restoring 40 sanity instead of 20. This leads to more psychosis casts and more RNG and more chances that Sara doesn't stop until you go completely insane...sigh.
Corruptor tentacles are always annoying. When phase 2 starts, it is a lot easier to use a macro to target the corruptor tentacle and cast Silence (if within range). Just spam the macro when phase 2 starts. Running towards a corruptor tentacle is another painful task, especially if it spawns far away. Angelic Feathers helps a lot, and is better than Body and Soul due to its 6 second increased run speed.
It is always preferable to get the brain down to 30% (to trigger phase 3) in one pass. I left the brain room early, thinking that my dots would finish it down to 30% before induce madness ends. Turned out it didn't and I had to do a second visit to the brain room.
Since Freya is active, there is no reason not to face the boss at all times, even during Lunatic Gaze. Simply restore sanity when running low. There aren't too many offensive spells a priest can use when not facing the boss.
Hodir was chosen as the keeper to be inactive in this fight since his ability is rather useless. If you need him to save you from a killing blow, you aren't far off a wipe anyway. The next keeper I would deactivate (if I ever do a Yogg+2) would be Freya, then followed by Mimiron.
Yogg+0 on 25man is still a ways away. But I can foresee him going down within this current expansion. Probably need heroic T16 gear though.