So, Malygos 25 man... I couldn't beat his enrage timer, so I merely survived it.
Goals: survive, get him to 50% at the last vortex before berserk.
Malygos will attack your pet. Don't stand in front of him because of his breath.
He will launch arcane bolts at you - drums of the wild and prismatic elixir greatly reduce incoming damage, chimera shot is enough to heal yourself.
The goal is to dps him fast and hard.
The fight repeats as follow after:
1-Vortex: summon your pet, dps malygos. You might want to use a misdirection.
2-Once you land, make your pet attack and feign death. Destroy the power spark, and get in it.
3-Blow rapid fire if there are more than 3 minutes before the berserk.
4-Ignore the second power spark unless you can stack it with the other.
5-Feign death as soon as it leaves cooldown to make sure it's available after the next vortex.
With this tactic, I could get him to phase 2 with 370 gear (365 gun).
If you're doing rather good, you might consider to slow dps at 53%, using chimera shot to self-heal. Slowly bring him to 50,49% (so it shows 50% if you're using percentage). Once he launches his last vortex, dps him hard. He should land, enrage, than fly up (he might try a hit or two - deterrence can be safe). He must enrage before the adds spawn.
Goals: survive the Scions. Survive the bolwfish test.
Dps as much as you can, unless you need to bandage.
Now, avoid getting killed by the scions. For that, do not FD too soon or too late: wait until the nexus lords gain aggro on you to feign death.
Then choose a Nexus lord, put your pet on him, without growl or misdirection, and dps while running, with rapid fire.
You should be able to dps and heal your pet this way.
When the Nexus lords use haste, feign death as soon as it comes off cooldown and finish the Nexus lord quick. Hop on the disk and fly up, possibly on a scion, before the deep breath (50K/second).
Now, you can ignore the nexus lords. They are extremely slow. The scions, however... They can and will aggro you if you get near them. So choose the nearest Scion, kill him. Then the nearest one, and so on. If you notice a scion attacking you, kill him right away. You can bandage while moving on the disk.
Then kill two of the three remaining lords.
Now starts the Bowlfish phase.
For more or less 25 minutes, you have to pretend you're a fish in a bowl, circling endlessly in a closed, blue space. Don't get bored. Don't Afk. Don't kill the last add. Nothing.
Just avoid going too low, Malygos's deep breath still hurts.
Goals: survive, dps, don't lose your concentration (like I did near the end).
Once Malygos stops being red, kill the last add.
Do not stay within 30 yards of Malygos!
Do it exactly like in 10-man normal: stack 5 HoT, then 1-1-2-3 while avoiding static fields (try staying at maximum range).
When you are low on health, use 1-1-4-3 (would 1-4-3 work?) to heal yourself up. Once you're at 100% health, start attacking again.
Rinse and repeat.
It's a very good idea to practise on Malygos 10-man, especially to understand when a scion will aggro you and when it won't.