Full breakdown of everything as I understand it:
"Do you know what tickles me most about all of this?" The thought arrives in your brain packaged and labelled as sound, but never existed as something so ludicrously inefficient as vibrating air. The past was simply changed so that the words had been heard. At the far side of the bubble of new space from the opening into reality, tendrils of magic wriggle through the thinned membrane that separates reality from unreality like maggots through dead flesh, and once they wriggle their way free they dissipate into will made manifest. "It's that every word I say will further excavate a warren of bad decisions that you will have to scurry your way through. Do you tell your little friends that you have thinned the one border of their reclaimed home that they cannot guard themselves? Do you tell them that you have been singled out for special attention by one of the Eyes of Tzeentch, the very one that once ensnared their brothers in the far north and begun the twilight of their race?"
It took only heartbeats for you to activate the Rune that flushes the magic out of the air, but entire sentences had already manifested themselves.
"What about your little magic club? They've already fretted about this very possibility, haven't they? Can they distinguish between a few whispered words and a full ensnaring of a soul? Could they dare to take such a chance that one such as you might already be suborned when you have the trust and ear of so many? Of course not. You already know what their response would be, because you've already delivered it unto another. The blood on your hands matches that on the crown on your friend's head."
Mathilde's experimentation with AV catches the attention of a Tzeentchian Daemon, it starts poking its way into reality through the pin hole that was opened
It immediately starts off by musing about how its very presence complicates everything and will make Mathilde doubt every move she makes going forward, and that she really has no good options
Does she even dare risk telling anyone about what just happened? At bare minimum they'll never trust her again if she does, they can't
Mathilde immediately starts flushing magic out of the tower
"The importance placed upon such pleasure, upon who has delivered them, grows by the hour. The First Betrayer sobs his fury for all to hear, knowing that the time will soon come again when he will crown one that might achieve what he could not and will never. Already the Four tally their joys and prod their servants, willing and not, knowing and not, into greater efforts. And do you know the most delightful part? That of all the promises and threats that have been whispered into the ears of the greatest and most terrible of champions, none have removed so many of their competitors from the greatest of tournaments than you."
This snippet is about Be'lakor, the first Daemon Prince who tried to play the Chaos Gods against each other and paid the price for it, impotently furious that he is fated to crown the Everchosen who might go on to become what he never will
The Four are already in progress of determining the 13th Everchosen, prodding and observing their various candidates, pushing them to compete with and eliminate each other to determine who will reign as the Champion of Chaos Undivided
Some of the candidates know they are prospective Everchosen, some don't, some are willing servants of the Four, some aren't
The Daemon then shares that Mathilde is of great interest to the Four, because she has unknowingly removed more competitors from the running than the competitors themselves
You stride towards the slit and gather your will and what scraps of Ulgu managed to cling to your soul.
"You have heard for yourself how exquisitely cultivated the resentment within Egrimm is, and seen how convincingly soothed his ruffled feathers now appear. You have tasted the millennia of curdled hate of the Briarmaven of Woe, and struck her down when she left her beloved shadows to finally act. You have known how blind Alric is to the unsuitability that all else know and sneer at, and you have thwarted his ambitions and eliminated his last chance to claw his way back into relevancy. You have felt your blade sing as it sliced through the Elector Count that demanded respect for a title when he had no part in the killings that brought it to him, and the knowledge that the one that thwarted him is also the one that has propped up two generations of the dynasty that usurped him will burn within him until the burning is all that remains of him."
You reach forward with your soul and bury talons of willpower into the newly-created fabric of reality.
The Daemon goes on to outline Mathilde's accomplishments, the implication being that these are all Everchosen candidates that she has fought in one form or another, and subsequently knocked out of the running
Egrimm Van Horstmann, not fought in the traditional sense but by spotting his resentment before it could boil over and helping him to get out from under Alric's thumb she's derailed his potential fall to Chaos... maybe (fucking Tzeentchian mindgames)
Drycha, fought and slain in the Battle of the Shirokij, it still doesn't seem likely that she's permanently dead but preventing her from achieving her objective may have had far greater significance than originally believed
Alric, thwarted his last chance to claw his way back to relevancy by slaying Alberich before he could
Alberich, uncovered and slain during the investigation of Talabheim, his soul in particular is screaming in fury and hate at Mathilde for that
Magic has been flushed out of the tower, the rift still hasn't closed
Mathilde moves to the rift and starts to forcibly close it herself
"And even now, my siblings bicker over whether you should be given credit that the brood that contained three generations of exquisite warlords that were so cleverly walked onto the precipice of apostasy, are now so utterly defeated that they will shriek and bite at any hand that reaches out for them, instead of allowing themselves to be properly usurped like their allies were."
Mathilde's quite the object of conversation in the Warp
Though in this case I'm not 100% sure what group its talking about
Possibilities come to mind but I'm not certain
Tendrils of the purest magic burrowing through reality seep into your now magic-starved soul and your grip on reality redoubles and redoubles again.
"Should you earn this world through right of conquest, your will here would be paramount. Not because you would be stronger than the Four, but because They want to see what you would do with it. They have worlds without counting where Their will becomes fact, and They have wrung every morsel of enjoyment out of such simple games. If you would take up the crown and with it make yourself the ultimate bulwark against Them, They would whisper and cajole and threaten and offer you every temptation to turn upon your wards, but every 'no' would be a rapturous novelty. All you'd need do to keep this world from their grasp is to stay true to your purpose. And is that not the founding purpose of your order? To be the 'no' in the darkness?"
You don't even know where to begin rejecting the strength that even the slightest wisp of the energies of the Changer of Ways has given you, and even if you could, it would render you unable to do that which needs to be done.
The Daemon starts its sales pitch
It knows Mathilde would not accept an offer to simply serve the Four, instead it puts forth the notion that she could rule this world in order to stand against them
That the Four would let her do this if only for the novelty alone, the Daemon claims they have countless worlds that they hold absolute dominion over, and that such simple conquest is boring to them
They could make a game out of sending forth every offer, enacting every plot, and watching how Mathilde resists and fights them, it'd be fun, games require adversaries after all
It's only asking her to keep doing what she's made her life's purpose anyway
With no magic in the room and barely any magic in her own body Mathilde doesn't have the power to close the rift
Then energy from the rift itself starts pouring into her, a gift from Tzeentch
Mathilde doesn't have the power to resist, and even if she did, that power is the only thing she has to close the rift with anyway
"Why do you think you were able to pull back so many of the generations born in Chaos from the Desolation Hold? Because the sweetest of victories was not those bludgeoned into submission and dragged off in chains, but those that would forge the chains themselves. A single sentry that walked into the darkness themselves and let the Maidens of Ecstacy have them delights the Four more than ten thousand who fight and bite and scratch and need their souls flayed down to the gristle before they obey."
Already chewed through by the tendrils of magic, it takes only a few tugs for your empowered will-claws to force the newly-formed walls of reality to buckle and pucker.
"When you can be sure of nothing else, be sure of the boredom of the Four. When they want puppets, they have as many of the likes of me as they could ever want. What they don't have is you. Should you be willing to change that, you could command any price. Every price."
The Daemon continues its sales pitch, it uses Karag Vlag as an example
Why was Vlag even still there to be rescued? Why did it even have a population of survivors that remained? It laid in the Warp itself for an uncountable length of time, its fall should have been inevitable, trivial
The Answer? Because the Four don't want broken puppets, not really. It's so much more gratifying when people willingly walk into their arms of their own free will. When their own personalities, their triumphs, their hopes and dreams, their fears, their flaws, their failures and their despair, pushes them to the Four of their own accord
To simply hold open the door for their new supplicant is so much better than forcibly dragging a soul into their clutches could ever be
So then what Mathilde has? Her ability to freely choose? That's a bargaining chip
The Four want her, but more than that they want her to walk across that line herself
And to that end she could ask anything of them, anything she could imagine could be hers
With the pick me up from Tzeentch empowering her, closing the rift becomes trivial
Reality itself bends
Scraps of reality's bloody flesh are pushed towards you by a sudden influx of the energies of the Aethyr, but they cannot flood freely into the world, because their point of ingress is contained within a bubble in the wall, and the only egress is the size of your palm. Like debris in a suddenly-narrowing river, as soon as one part of it snags it causes a pile-up of the rest, and in a moment a portal becomes a scarred pucker, holding fast against all that would press against it. This stops the tendrils, but it cannot stop the last whisper already planted in the past.
"You cannot prevent the emergence of a Thirteenth, just as you cannot prevent the existence of Ulgu. All you can do is decide whether such a weapon should be surrendered without a fight to the whims of the vilest."
As the rift is sealed the Daemon leaves one last message
It promises that the 13th Everchosen
will rise, she cannot stop it
But if she wants another weapon to wield against the End of The World well... she need only ask
After all, Ulgu itself came from the Realm of Chaos and yet it is undeniably a part of her, a part she would never willingly give up