Thwarting the Twins

This quest starts the scenario that leads to obtaining the challenge appearance for your artifact. Currently, these scenarios are incredibly difficult to the point where it might genuinely be impossible to complete unless you're better geared -- and by 'better geared,' I mean 910-920+ ilvl. Don't expect to make any headway until Tomb releases, is what I'm saying.

It would've been very nice to have the above communicated in-game before you were one-shot and came here to figure out what happened, but oh well.

(forgive me for not using links to spells and stuff)

Phase 1, you want to kite karam around and just avoid getting hit while dpsing him to ~35%.
Karam gains a stacking buff the longer he is in combat with you. increasing his movement speed, and damage.
He is subject to diminishing returns so you cant just spam roots or anything every 3 seconds to get distance.
He also appears to be immune to stuns.
at Approximately 35% Karam will become immune and cast purgatory which heals karam to what Ive seen approximately 85% health or so. It appears to be timer based, This starts phase 2

In phase 2, Raest is targetable and will begin casting shadow bolts at you, they don't hurt too much. and he can be interupted. depending on your class(boomkins) i advise against it.
He will also summon 4 or so packs of shadow fiends, these do hurt. you want to simultaneously kill and kite them while also attacking Raest.
The best I've gotten Raest down in this phase is 75-76%, i even used hero in here in an attempt to push him further, it doesnt seem to make a difference.

He'll then go into Phase 1 again with added mechanics
Back in phase 1, Karam resumes chasing you down with his stacking movement speed buff. only thankfully he's not at full health this time.
Raest will now summon creatures called Hand from beyond, they can spawn anywhere on the entire platform, and if youre not quick, will murderize you.
They only have 5 million HP, but they cast a spell called Grasp from Beyond. which deals 4 million damage to you. It appears to be mitigateable to an extent.

once karam hits ~35% again you'll get into a second and final phase 2:
I'd suggest a drums here.
This time, the hands will will still be summoned, and now he summons rune/balls that summon some void guy like general Vezax from Ulduar. They will murder you so ensure you soak this rune.
Once Karam finishes his cast, he will begin chasing you again, but Raest is still targetable. Continue to kite Karam while soaking runes and killing hands immediately. karam is your lowest priority target, just keep him away from you.
When you kill Raest the hands still seem to spawn(maybe a bug?) but you still have to kill karam, no other mechanic will exist. once you kill karam, any active hand will despawn and a portal pops up where you entered.

I wrote this in the hopes that someone can use this info to finish this quest. To be honest, this might not be doable for many until heavily ToS geared. So if you cant finish at this moment, I'd suggest just waiting. it'll be available later.

Through enough different strats using people from Boomkin Discord(a guide ended up being posted for talents and such) I just finished and man was it nerve racking haha.
As a boomkin if you have them available to you, i would suggest running [item=137015] and [item=132452], with the talent choices of 2,2,1,1,1,1,2. This gives you WoE for burst LS, fancy moveable casting starfalls, and a lot of speed. I pooled Astral Power before first hand came out, Bashed Karam then popped WoE, both dots (4 set buff) spam SS, then LS and more SS as necessary to finish the hand. the next hand I Solarbeamed the hand and bursted it down. Then rinse repeat for every other hand.
This method took me 7 attempts last night to give up, and 5 attempts tonight to finish. Still a tough encounter for sure, but doable with enough skill.
Hope I helped out guys

EDITED using bossfight1's comment after more testing while watching closely proved myself wrong on the puddles!
EDIT for final strats I used to complete as a boomkin

Karam and his brother Raest, is a reference to Caramon and Raistlin Majere twins from Dragonlance saga.
The Caramon was a warrior and some times portrayed wearing plate armor with "wings" on the head piece and Raistlin a neutral and then an "evil" black robe mage much like he is portrayed in game also.
Caramon also used to call Raistlin, Raist thus Reast here.