Raku

The Master of masters calls Xehanort "the Singularity" in the scene where saves him in the dark corridors. Chirithy says that Sora will lose his powers if he goes too far with the power of waking, which he does, and it makes him vanish. If I'm right, that just might be the reason why the Master and Strelitzia haven't come back yet,they both might need Sora to come back,since Sora is seen summoning his kingdom key in Quadratum in the kh4 trailer. It might seem like the Master is an antagonist, but it's more like he's devoted to his plan. He's taking necessary steps and sacrifices for the greater good. In Dark Road this theme is lightly touched upon. It's a matter of perspective. But he does harbor "Pride", so he will most likely be a boss at one point or another. The calamitous star is term mentionned in Missing Link, and there's absolutely nothing official that ties it to Brain, that's part of my theory. Thanks!
 
Edit: Sorry, I tied the calamitous star term the Brain, because he's an anomaly, and the societies in that era hunt down what they think are discrepancies in the book of prophecies.

You're right, there is no real way to tell if that character is Skuld or not. The girl Lea and Isa want to save could be her too, or, it could be the white robed person Luxu sent to the future, he is the one who broke her out of Radiant Garden as Braig. The Data-Copy of Strelitzia maybe? I can't wait to see for myself honestly 🤣

I like the theory. My only pushback would be is that we don’t know if that’s actually Skuld that was holding the baby Xehanort. It could be a new character, possibly a descendant of hers. Also we still never found out if skuld might’ve been the person that Lea & Isa found. Other than that one part tho I dig this a lot

Thanks for writing up this theory, can tell that you put a lot of thought into it.
I'll preface my post by saying while I've played KHUx the main story was scattered so far apart between updates it's a bit of a blur for me to remember, same with KHDR, and with ML I haven't looked into the story leaks yet, even though I know they're floating around online. So just bear with me and help me fill in some gaps if I'm not understanding correctly. I'll do my best to add to this discussion. 
So basically you're thinking that Brain is the Master of Master's. There's a few concepts I don't quite follow, where does the calamitous star and singularity come from? Also trying to understand where MoM would take Sora back to, and for what purpose. Brain never struck me as an antagonistic or shady character, and from what we know seems MoM will be the antagonist going into the next saga, so just seems interesting to me to have that revealed to be him. 

I was hoping to have a good ol' fashion theory discussion as to where the series is going, and the who's whos, and what's whats. Let me know what you all think. At the very least I hope it's a good read.
In the first go around, where time is not altered by anyone, The Master of masters and other beings of light were caught in a war with beings of darkness. The war went on and on until the beings of darkness shed their physical forms and started infecting people from within, which eventually caused the world to end. The Master of masters, and "Darkness" seem to be the only survivors mentionned. The Master was not willing to give himself as a vessel, and the Darkness was losing its will without a vessel to give it form, they had many conversations and battles, but both determined they were at a stalemate. After learning everything there is to know about keyblade wielding, and after witnessing the end of the world, The Master of masters decides to commit the ultimate taboo.
The Master of masters dives into the sleeping world of Daybreak town,while there, he notices that his friends along with a past version of himself are trapped in a loop where the keyblade war repeats itself over and over in the world's sleep, coming to the conclusion that the war is the key event that plunges the world into darkness, and comes up with a plan to avert the destruction of the world all the while respecting the laws of the flow of time. But first he would have to abandon his worldline.
In preparation, he crafted a keyblade and implanted his eye into it, and with it, observed all of the events that lead to the war. He manages to leave the sleeping world along with 6 keyblade wielders, 5 of which were to be the leaders that participated in the war, the 6th was the Master's past self,and they headed for a new worldline.
Once there, they are given new names, and each a keyblade crafted from their hearts, and are trained to be keyblade masters. The Master writes 5 copies of the book of prophecies, and gives 5 of them a copy, detailing the events up to the keyblade war, which is imminent, but leaves out critical information, full knowing he's being watched as it is being written.
And so, they are dubbed the Foretellers. Because they are in a new worldline, this new worldline's version of the people who were to become the Foretellers, are spared that fate, and live their lives as members of the Foretellers's unions instead, so the Foretellers wore masks and robes to hide their identities.
When the time came and preperations almost complete, the Master wrote another copy of the Book of Prophecies. To his delight, the future had changed, confirming that his plan would work. And it too, was watched as it was written. Knowing himself and his own follow through more than anybody, the Master bequeathed his keyblade to his past self, giving him his role, special instructions, and revealing the fate of the Dandelion leaders, in doing so, he ensured that the future would change, once again. Once Luxu leaves, the Master gives the Foretellers their own roles, rips a page from the new copy, dubbed the Lost Page, and gives it to Gula. Upon speaking with Ava, the Master gave her a special role, which had her found, and recruit all the members of the Dandelions, including their leaders, who, unknown to Ava, were the people who were this worldline's versions of the Foretellers.
Ava, noticed this book was different to her own. Sensing something wrong, and inspired by a speech made by Ephemer trying to cheer her up, she decided to follow her own heart, just as Luxu does. She gives the last copy of the Book of Prophecies given to her by the Master meant for Ephemer to Brain instead, and leaves a memo in the book with the names of the leaders the Master had outlined. This was done after this copy of the book was written, and so when the future eventually changed,the book did not contain said changes, just as the copies the Foretellers had ended with the keyblade war as their last pages. This crucial piece of information,and Luxu's intervention is what lead Brain and the others to eventually avoid their fate as vessels of the 4 darknesses. The moment Ava gives the Book to Brain, is the moment The Master vanished just like Sora did, although he was busy before he did, like speaking with Xehanort in the future. His plan changed history, and he crossed into Quadratum.
The Foretellers maintain their unions desperately clinging to their Master's teachings and the conflicting roles he imposed on them, inevitably causing the war, the Foretellers are lost along with 5 of the 13 Darknesses. 
4 Darknesses, were sealed inside the data world's borders without their intended vessels. 1 Darkness was sent to the future within Ventus. 1 was set free by Maleficient, another was inside of Luxu, while the strongest was sealed within the Master.
The keyblade war came to pass, ensuring the flow of time. And the Dandelion leaders are spread out across time, and unknowingly fulfilling their Foreteller counterpart's roles, although in different time periods, but still fulfilling their destinies etched within their hearts.
Brain gives the last copy of the Book to Ephemer, the rightful heir, before a meeting with man that had the same face he did, it was with this black robed doppelganger's help that he was able to escape Daybreak Town's inevitable destruction while still being able to help Ephemer, Skuld, Lauriam,a stowed away Elrena and a comatose Ventus to the future. This was Luxu, who later penned that he claimed Brain as an imposter, probably due to him looking exactly like him, but the imposter was actually Ventus.
Ira's role of becoming the leader while the Master is gone was fulfilled by his counterpart Ephemer, who founded Scala ad Caelum, his descendants also became powerful leaders, like Master Odin, and Xehanort and all his incarnations.
Aced's role "One day, you might think, ewww he stinks at this, in which case it will be your time to step up... You never know, your leadership might just be what everyone needs". This is fulfilled by his counterpart Lauriam, as Marluxia when he tries to stage a coup against Xemnas, which makes Xemnas hasten his plans.
Invi's role as mediator, and making sure everyone gets along. Is fulfilled by her counterpart Skuld, who, whisks away a baby Xehanort from Scala ad Caelum.
Ava's role will be fulfilled twofold, once as Ava, recruiting the dandelions as a separate organization. While her counterpart Strelitzia, will fulfill this role by helping Sora and Riku back from Quadratum to keep hope alive.
And finally, Gula, his role was to find the traitor outlined in the last copy of the book made by the master on the Lost page. As Gula, the traitor was Luxu however it was too late, and he failed to find him, he still wasn't sure who the traitor was when he perished in the war. His counterpart, the Player, in his 2nd life fulfills this role, and finds Xehanort before it's too late. And ends up raising him.
Luxu's role was fulfilled by Luxu himself. Passing down the Master's keyblade and standing by until Xehanort inherits it. Recording the future, so that the Master could see it.
After Scala ad Caelum was established Ephemer realized that events he had lived through in the past were not inscribed correctly in the copy of Book of Prophecies he had received from Brain, and concluded that the Book had False Pages. And so he founded new unions, called societies and their goal was to uncover the truth and expose the False pages within the Book.
Xehanort's role as the Singularity, can be explained by having a connection with all those involved, especially Ephemer.
In the end, the Master will return after the X-Blade war, only after all 7 of these roles are fulfilled. Xehanort has already reenacted the war. Strelitzia just needs to bring Sora and Riku back to fulfill the last role. And the game between the Light piece and 7 Dark Pieces will begin.
What I'm getting at is that the Master of masters was the Brain from the Original worldline, Luxu is his past self, and Brain is the very same person in the new worldline, who re-appears in the Blank Age as the calamitous star, because his descendant, Eraqus, becomes Xehanort's best friend, is responsible for training Aqua, Terra and Ventus, and in the end helps Xehanort concede defeat and give the x-Blade to Sora, which further changes the future.
But ofcourse, the Master foresaw all of this, and is waiting for Sora in Quadratum. So he can come back with him.
But yeah, that's what I think is the premise of the Lost Masters Arc. Thanks for reading, and let me know what you think.

Ohhhhh
Just did a very quick search and there's suggestions that Lodur could potentially be another identity of Loki

Dark Road will lead into th3 beginning of BBS. What if we get to see how Terra & Aqua meet too.

a time travelling vanitas?

What Ocean's Rage said. And it would be cool if we got to see a young Yen Sid!

no, brain was the one whos name was circled in red and ven is the only one whos name wasnt on the list

Everything I've seen and read so far is making me want this DLC more and more. I wonder if KHUx 's updates are gonna start rolling out faster to coincide with the DLC's release? To be completely honest, the Bosses and the new scenarios and cutscenes are already enough for me, I mean who knows what kind of cliff-hanger we're in for... Mirage Arena-ish world would be cool, but i'm kinda hoping they incorporate a new area for the new stuff like Cavern of Remembrance, with high level baddies and tricky platforming.

To be fair, STR traits are still worthwhile, but only the +1000 and +2000 traits. Anything lower than that (which comes from pet training) is worthless. It's a good idea to mix the ground/aerial def traits with STR traits, as well as Extra Attack traits (and raid traits if you plan to use the medal for raiding).
DEF traits are the least useful, with HP traits being a close second.

Nomura responding to a question about Xion's return by saying he will expand upon it in the DLC doesn't indicate she will be the central focus.  I think it's more likely we'll be getting the final mix treatment.  Limit Cut" sounds like it might mean Director's Cut, which would be additional scenes throughout the main story to flesh out the plot a bit more. 
 
We need more backstory on Scala, Xehanort, Eraqus, and their Master more than anything imo.  Seeing as it is the end of Xehanort's arc, and everyone else's subplots can be explained in future games.  This is it for Xehanort's story.

Well, the events right now have prizes that aren't extremely necessary, so don't beat yourself up too much if you can't complete them. The expert level stuff usually requires extremely good medals with very specific traits. If you don't have ground def -60, for example, you won't do much against a lv. 5000 enemy. The reason for that is because your strength has to overpower their defense, and the only ways to do that are to have a high strength stat (primarily from your supernova medals), use all available buffs/debuffs (atk up for you, def down for them), and have either ground/air def -60 (depending on which type you're facing). If you're able to hit all of those points, it's hard to say why you wouldn't be completing the events.
As for setup advice, you'll usually want to use Starlight, Stroke of Midnight, or Fairy Stars (make sure they're at or around lv. 35). Your buffer goes in the first slot, preferably something like SN KH3 Kairi or SN Xion. After that you'll want to follow up with damage-dealing medals that make up for any buffs/debuffs you haven't already covered (for example, the 2 I mentioned only do +12 PSM atk). You don't have to match your buffer medal to the slot multiplier (you don't have to put a power medal in a power slot, in other words), but you want to try and make sure all of your damage-dealing medals do match the keyblade slots. Your most powerful medal should go in your pet slot as that is the highest multiplier on any keyblade you use. Oh, and make sure you have a high subslot value (using those 7-star medals you mentioned).

Hmm, I'm not familiar enough with ux lore