Mecheon
Sacabambaspis
Pteranadons, if assuming a male P. longiceps (Because of course there's that lovely debate over where P. sternbergi fits) are kind of eehhhh mount-sized in my opinion
Now, if your player wanted to truly be Op he would go with the king of the sky, the mighty Azdarchidae Pterosaurs such as Quetzalcoatlus which were the size of giraffes and ate anything smaller than them, along with being part of the pterosaurs who were more about being on the ground than flying
I mean, it could fly, but this was the type of thing that flew in order to find somewhere to land and start eating
Now, if your player wanted to truly be Op he would go with the king of the sky, the mighty Azdarchidae Pterosaurs such as Quetzalcoatlus which were the size of giraffes and ate anything smaller than them, along with being part of the pterosaurs who were more about being on the ground than flying
I mean, it could fly, but this was the type of thing that flew in order to find somewhere to land and start eating