This is very late, but necessary, I think. Cat has with him both his horse, Syracuse, and his baby griffin, Klartch.
Syracuse is described as follows:
Syracuse was a dark brown that was nearly black, with a swatch of midnight for his mane and a flying, silky black tail. His head was shapely and proud. He was a perfect slender, muscly build of horse, and his legs were elegant, long, and deft. He was not very large, and he moved like a dancer as he jinked and dodged away from the running, shouting, clutching humans. The Chronicles of Chrstomanci, Volume III, pg 376
He is also recognized as having some unicorn blood. He's notoriously difficult, and as such, if your character has spent any time near the stables, he or she has probably learned to carry peppermints for his appeasement.
Klartch:
Begins growing very rapidly, as a result of the stasis spell on his egg and how long he was inside it. And, as Chrestomanci says, because he has a lot of magic. However, for manageability, since the City does dampen magic, I am assuming that the City has worked itself on Klartch and his growth has slowed some. That said, he is now a little over two months old. [EDIT: Er, obviously no longer the case! But!] He is beginning to develop a vocabulary, and may speak from time to time. His appetite, despite his reduced growth, remains quite large.
Descriptions from the book, during his early stages aderpderp:
In the morning, it climbed out of its basket and woke Cat by nudging him with its beak. Cat opened his eyes to find two yellow griffin eyes staring into his, interested and friendly. ... There was no doubt that it had grown again in the night. The dark beginnings of feathers were showing on its neck and on its absurd, stubby wings. ... The griffin was such a plump, scrawny, unfinished-looking creature. It still had not gotten the hang of walking. It rolled from side to side, scratching the stones of the yawd with its long pink claws, and whirling its stringy tail behind it. ... He was also growing an odd small tuft of feathers on his head, like an untidy topknot. The Chronicles of Chrstomanci, Volume III
Off hand I can't find where he's described as having grey feathers. Also the author in one passage states that Klartch has front paws, and another that he has front talons, so idfk. Let's go with paws because that's what art shows.
I would imagine at this point that he's grown into himself a bit, to look a LITTLE less awkward. More feathers. Slightly better walking. And so forth! Because his aging had been slowed, and he is a baby. ... I like to think of him looking like
this, ONLY YOUNGER, less feathers, grey, etc.
Klartchball! Klartch is PLAYFUL. There is a game. Cat fails hard enough at explaining things. So if you ever partake in Klartchball, it is described like this:
... Cat picked up the football and, after thinking hard, managed to mend it, blow it up again, and make it griffin-proof in future. Then everyone, even the head gardener, joined in a game that Janet called Klartchball. The rules were a little vague, and mostly involved everyone running about, while Klartch galloped and rolled and tripped other players up. It was such fun that Roger and Joe emerged from their shed and joined in for a while. The game only stopped when Klartch suddenly stood still, hunched himself, and rolled over on his side in the middle of the lawn. The Chronicles of Chrstomanci, Volume III
Lab:
The poor pig had exchanged hands quite a bit until the Pevensies gave him to the Chrestomanci trio. He is pink with black spots and quite a gentleman.