So, dissecting the lies here, because there are some pretty good ones, and some pretty mediocre ones, too.
"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?"
And here we have the first lie, and the most pervasive one- that there is no escape from the plots and plans of Chaos, that their power and ability is so great that it's impossible to truly defy them. Some of the decisions here are worse, and some are better.
"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."
Sure, they've worried, they probably worry about every wizard who achieves even a fraction Mathilde has. And yes, they can distinguish between being exposed/tempted and being ensnared - Mathilde proved it herself on the way back from Karak Dum, with Barbitus. It didn't even take more than talking, and a bit of logic. Clumsy, there.
And comparing her to Alberich is also clumsy - he was in the end stages of a murderous ritual of dedication, had already taken many steps down that path, and was clearly not redeemable.
"Do you know how much effort it normally takes to craft a platter of truth and lies that will so haunt a mortal that they will spend the rest of their days trying their best to decorticate it? But you and yours who have so wonderfully usurped the Sword of Tlanxla have so twisted your own minds that I could say anything or nothing and you will dwell obligingly on it forever. If I said 'I like your hat' - and I really, really do - you will wonder, is this an example of the pettiest of statements for you to nevertheless obsess over, to demonstrate that I can command your mind through only your ears? Or am I making a deeper statement about how truly it pleases the Lord of Sorcery for a witch to wear the garb of those that would hunt her? Am I masking truth in lies, or lies in truth? Would it only be a truth if you decide it a lie, or only a lie if you decide it a truth? Or is eternal indecision that which I seek?"
Blah, blah, garbage, I have good taste in hats, blah. Sure, it might tickle The Plotter's fancy for the irony there, but otherwise it's back to the first lie. The response to the unknown does not need to be indecision.
"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."
And here's another probable lie, by stating a truth in a way that implies more value than is known. Sure, the time when a new Everchosen approaches, hour by hour... as it has been since the last one was killed. And actually, that Mathilde has removed more than anyone else of contenders suggests that the winnowing process is still very much in the early stages. (Assuming that's not a more blatant lie.) Still, the flattery is nice.
"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."
Meh. It's always possible Egrimm is hiding something, but at least just as possible that his ruffled feathers are
actually soothed, not just as a show. I don't know enough about Drycha to say, but... well, Athel Loren. As for Alric... meh, handling him is Other Peoples' Job, and this might be a bit of misinformation along the lines of "he's really a very low-probability candidate". And Alberich was not an Elector Count*, he wasn't demanding respect for the title, and the Van Hal dynasty only usurped him in his deluded fantasies.
*Well, he was at one point, but I'm pretty sure that being declared "dead or worse" means you lose the legal title.
"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."
Who should it be given to? Ljiljana and her gods? That would also be fair. They sound like a bunch of grumpy kill-stealers.
"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?"
And, yet another lie - or at least, it's a promise of power with the not-too-hidden threat that if the Four ever felt like it, they would take the world anyway. Becoming too "boring", or whatever other failure they thing qualifies, and... yeah.
"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."
Back to the first lie. Sure, the souls who willingly went to Chaos were likely considered more prized, but the idea that they
let Mathilde pull Karak Vlag back... it's the usual bit. Yes, they could have done more to try to stop her, but
at what cost to their other endeavors? And would it have been enough anyway? (I suspect the answers are "a lot", and "probably not".)
"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 lie: "And once they have
you, anything they give you is still theirs."
To quote Lois McMaster Bujold: "The one thing you can't trade for your heart's desire is your heart."
"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."
Becoming the Thirteenth Everchosen is not a weapon. It is a betrayal of
all of Mathilde's loyalties.
Now, going to the competition, killing all the others, then flipping off Chaos and walking off would be a major power move, but I suspect that would result in getting smited by all Four.
So, yeah. Very little useful information, and a bunch of deception that someone with Mathilde's Intrigue would probably be able to parse out quicker than I could. Which actually seems exactly right for a minion of the Plotter.