The undeniable, infallible proof, is that there's no way for one to imbue permanent magic into something or someone, and there's no way a Monster would be able to wield magic in the way that Witches do now! It just isn't in their soul, you know? Their being. A Dragon can eat magic all day, for example, but it isn't as if their breath -- which isn't magic, by the way, it's just a concentrated amount of energy, hogwash anyone who says otherwise -- grows ever stronger, so the rumor of "True Fae" is just absolute poppycock... Georgie'll be more than happy to show him his files and folders regarding these facts at another point, he simply needs to buy new yarn to connect the latest points.

Regardless. The account.

There's more or less a straight shot into the middle of the continent following a river that feeds into the sea, and so a large company comprised of trained Witches, medics, researchers, Monsters, and record-keepers followed it as far as they could, and set up camp in the thick of the woods there, around an hour's walk on foot or so it's written. There they wrote of the very things that Eren'd mentioned, the state of the flora surrounding the base, and kept a record of cures they tried whilst maintaining the camp to see which was most effective in "curing" the Cwyld, many techniques which are still used today by the Wilders.

Time, Georgie explains, is odder the more you traverse into the Wilde, be that the seasons are switched as is and so the hours feel off as well, and many of the things are guesstimates. The only way to track it in the Wilde proper was to count by the visible seasons, and to know if you went in at the beginning of spring elsewhere it would be the beginning of autumn, if you left in the dead of winter there you'd arrive home in the heat of summer. That sort of thing. Following this, he says that it was at some point that autumn there they felt confident enough to try to dig deeper into the Heart than ever before, having been stopped prior by unlucky happenstances such as minor infections, equipment faltering, so on and so forth.

On this expedition of ten were Thrush and Moore, the former being a medic in training and the latter an inspiring journalist of sorts. Record-keeper. Archivist. So on, so on. What Monsters they brought along for protection unfortunately either died or had to be put down due to the Cwyld infections they held, and there'd be little word of what happened to the more brave researchers and Witches as well -- though Georgie's of the mind that they'd been taken and consumed, and there's doubtlessly craters to prove that within the area known as Dewaint in the oldest of archives. T'was these two and three others than returned to camp, and those three were...

Well. They were put to rest almost immediately, despite Thrush and Moore's efforts to save them prior. It was just too dangerous to keep them around. Thrush held more of the infection than Moore did on her part, but it wasn't to a level that would be harmful to remove, and the true scarring to their person was mental. Reports mention that they wouldn't speak for days after unless to ask after the companions they'd left behind and the ones they'd brought back, and it'd only been once they arrived back in Aefenglom that the Dreamers of the time were able to calm their minds enough to ask, to probe their memories for truths.

However, due to the amount of mental trauma they'd faced, the memories weren't of much help. Darkness and blocks that, when removed even a smidge, sent the two screaming. What was retrieved from these attempts, paired with interrogation, was just as Eren said: A Cwyltid unlike any other, something that'd been a Monster and was one no more.

Something interesting between Alissa's account and this, however, is the lack of mentioned crystalization, as well as no mention of any drawings nor guesses as to what the Cywltid could've been.

As for the question of chimaera, it's possible. There's all sorts of combinations of creatures, but Georgie doesn't see the connection between that and the records.