For natural animals, you don't necessarily *need* a unique stat block.
Since they are about the same size and as far as we know have similar abilities, for the compy, I'd just use the stat block for the cat in the Monster Manual, maybe dropping the racial bonus to Climb since it's not apparent that compys were tree climbers.
Other than that, if you remove the name "Cat" you are left with a Tiny animal that is fast, agile, has claws and teeth, hunts at night with its low-light vision ... sounds like a compy to me.