That fight looks atrocious on the streams i've seen just fucking woble goble of ability's.
So what are the changes to Mythic? Other than abilities overlapping? 2 big meteors? 2 soak beams?
2 Big Armagueddon, 8 small one.
The Erupting reflection (spawned by DPS) cannot be stacked (they deal way too much damage and heal other reflection nearby when killed). The player that spawned the erupting reflection will emit a lot of little orbs when the his reflection dies. (Those orbs deal a lot of damage and knockup player hit).
The knockback on the Rupturing singularity is WAY stronger compared to heroic. For example, if the rupturing singularity is in the middle of the room you WILL get knockback out of the platform regardless of where you are standing at the impact (unless you have a blink ofc). So to counter this ability you need to use a new mythic mechanic:
The tank reflection (that is now present in P1 btw) will put a debuff on the tank after it dies. This debuff last forever or until dispell, and when you dispell it ALL the raid is pulled towards the tank (basically a friendly mass grip). So you need to dispell the debuff at the right time to counter the big middle knockback (it's pretty impressive when pulled off).
For first intermission: no ability changes from heroic, but you have WAY more Rupturing singularity dropping (like sometimes 3-4 in quick succession). So basically all the raid is getting bounced around (remember the knockback is brutal).
P2: all the abilities of P1 + big beam and bursting flames. New mythic mechanic is the healer reflection. All the healer spawn a friendly add that can be heal up. After a while each add deals raid wide damage and spawn a void pull under them (that deal ticking damage and silence everyone in it). The damage and size of the pool depends of how much health the adds have (you basically need to heal them to full).
Second intermission: All we know for the moment is the fact that Rupturing singularities are casted during the dark phase... Hard to see them
P3: all we know is that the demonic obelisk deals WAY more damage (around 15million according to dungeon journal). So it's basically a one shot if you get it and you don't have an immunity.
if you want to see the encounter in action you can watch Alpha on twitch https://www.twitch.tv/vizoukgg (look at their replays if they are not streaming). Best pull 39%, with around 1000 wipes. They reached the second intermission twice.
Edit : maybe i forgot some things, so feel free to correct me
There was literally ZERO difference mechanically until phase 3(4 depending on how you count it). The only real change was the special abilities could only be used once. It was the rearrangement of phases and overlapping of mechanics, thus forcing you to do the fight completely differently, that actually made it different.
I mean but altering a mechanic such as how they altered the special button does so in a meaningful way that doesn't just add more difficulty for the sake of being difficult though. It's something to work around. KJ mythic just seems like they looked at it and said "Hmm, how do we make this boss a bitch to kill? Let's add BULLET HELL... and uh... 2 BIG SOAKS.. and uh... I know... what if we royally fucked the players over by making singularity happen during the second intermission phase?"
I know that it should fundamentally be the same but it's like... not really adding anything meaningful to the fight or altering the fight in ways that make you stop and think. Just feels like they pushed the numbers up and tried to fuck over players. Like... Shadow Traps in Lich King phase 1 made things harder by forcing you to be mobile in a phase where you didn't move on normal, but it does so in a way that feels good. Like... the Lich King adds could spew out a bullet hell every 30 seconds and that would force you to be mobile but it's just like... a huge scramble and not something you can really plan around or something that really makes much sense in the context of the fight.
Also what is it with this expansion and Blizzard making things that explode when they die? Arcway has those spiders (which they thankfully changed to have a timed explosion on death), Demonic Inquisition mythic has those adds that explode when they die (thankfully also timed but slow classes really need to move out and be mindful of their health at all times when it's low because the radius is big enough to where you won't be able to walk out in time if you're too close when they die), the little adds in the downstairs phase of Desolate Host which explode and do a knockback when they die, and then KJ mythic has adds that explode into bullet hell. Maybe I'm too old fashioned but I much rather enjoy adds whose corpses linger with a negative effect somehow and must be killed in specific spots to avoid death rather than "Oh this thing is low on health, time to run away like a bitch until it explodes"