The wildlife in the North Central reaches differ quite a bit from one side of the great valley to the other; both the Yuan-Ti and the Lizardfolk strongly control which creatures live in their kingdoms, based on their own religious beliefs and taboos.
On the Yuan-Ti side, you can find:
Yuan-Ti, obviously. They have giant nests (their equivalent to towns and villages) throughout their empire, both underground and through the giant trees.
Snaketongue cultists and Histachi, the servants of the Yuan-Ti
Shambling Mounds, Vine Horrors, Battlebriars, etc
Snakes of all kinds, both monstrous (Deathrattle Vipers, Crushgrip Constrictors, etc) and regular. A far, far greater amount than is found in any regular forest/jungle.
Spiders of all kinds, both monstrous (Deathjump, Bloodweb, etc) and regular.
Most kinds of giant vermin
On the Lizardfolk side, you can find:
Lizardfolk, obviously. High-class lizardfolk live in temples strewn throughout their kingdoms (think Aztec in nature), whilst common lizardfolk simply live in tribes in the wilderness.
Trolls, who have a loose alliance with the lizardfolk
Monstrous crocodiles (visejaw, feymire). Much more than would be found in a regular forest/jungle.
Drakes of all kinds
These lists aren’t mutually exclusive; creatures from either side can be found in the other, but are much rarer.
In the other jungles can be found a much smaller amount of the above creatures, as well as:
A green dragon or two