u/Embarrassed-Top4511

For a start, do not treat your hybrid like it is going to be a horror villain (even though some animals fit that bill) treat it as if it were an animal, because Hybrids do exist on planet earth, like Mules, Ligers, or Pizzly Bears, but a handful of them are able to reproduce, such as the Pizzly or Wholphin

On top of this set it up as if it were Speculative Evolution, so that it is more grounded, if your hybrid has a sail, say it is for display or thermal regulation, if your hybrid is large, say it is for intimidation or so that it could better protect itself, even though that is a genetic addon from an animal that has already done it

And finally sizing, modern day earth is not like cretaceous or carboniferous earth, the oxygen level is lower, so for your animal to be big enough to live, give it a evolutionary loophole, Mammoths and elephants reached such sizes because they adapted legs to support them, and Whales can get away with their size because water is far denser yet if they went on land they crush themselves and become beached, this could happen to T Rex in the modern day, even though it is nowhere as big as a whale it is too big to support itself due to the lower oxygen and improper legs