My regular party ran across some “dire” creatures some time back, and in the interest of developing a clearer mental picture, someone looked up exactly what that meant. Nerds, you know.
Anyway, the description we found then, and still use now several years later, is: larger body, smaller brain.
Apply that to any dire animal, and you’ll get an apt description. A common wolf would strenuously avoid a regular party of adventurers tramping their way through a forest. The wolf would probably see, hear, and smell them from a long way off, and maybe even sneak up to take a look, but unless the adventurers stumbled across its den, the wolf would mostly likely avoid them like the plague.
A dire wolf is bigger and more dangerous, but also not burdened by such a strong sense of self preservation, making it more likely to attack a bunch of humanoids without provocation. This makes them ideal fodder for RPG parties. Big, dumb, dangerous, and likely to attack for no good reason.
Imagine your dire cat fitting that schema. Big, mean, dangerous, and dumb. But unlike wolves, big cats like lions and tigers won’t think twice about attacking a group of people. So a dire cat has to be even more dangerous and unpredictable than a pride of lions.
When creating any “Dire” creature it isn’t enough to just make a larger version of a dangerous animal. You must keep the psychology of the animal in mind. How will the creature’s behavior make it more dangerous than a standard version of that animal? Will it be more likely to attack the strongest in your party, or the weakest? Will it rely on its larger form for protection or will it want to pick off your party one by one?
These are the questions you must ask yourself when creating “dire” creatures for your game. A little bit of forethought will make for a more interesting and more entertaining creature for your players to defeat, or be defeated by.