There already was something like this, Andrewsarchus, it is even related to hippo.
large crocodile like head, that is a good a description as any unscientific culture would come up with.
Lion like mane and tail, check on the tail the main is anyones guess so go for it.
being as large as a hippo, damn close
being carnivorous and likely being scavengers, easy check, that is true for basically all predators.
having scales on their face, this is the hard one hair ans scales together is basically impossible unless it is decended from pangolins. But it could be scale like in appearance, scale like lumpy skin has evolved more than once in mammals.
having claws on it's forelimbs and hippo like hindlimbs, check on the claws but for the second this depends on what you mean by hippo-like, the hind legs are shorter. It is closely related to hippo so you have that going for you. There is a lot of different interpretations of what it looked like just because it is so closely related to hippo. Plus they come in several sizes.