Okay, yeah that makes sense. What's a reasonable amount of skills for him to have? Should I give him aspects, too? How would you recommend I handle the command skill?
Just make the tiger like you would any other PC, otherwise it will be pretty weak in comparison, and I'm sure the player would want a powerful sidekick. Just adjust the opposition for an additional pc.
If you give the tiger character to the player, I wouldn't make the player have a skill for that. Just a high concept like "beast master" or something, that makes it reasonable that he can communicate with the tiger would be enough. The tiger would be more his friend and companion, than his pet.
If you as a GM take over the tiger, I'd give the player an extra skill like "animal handling", and judge how the tiger reacts to him by how well he rolls on that. The player can then use an action in a fight to give the tiger an order, and the tiger will do as told.
I would prefer the first method, because it makes the tiger an actual and interesting character, and that is way cooler than just making it an attack bot. The player could decide to take the tiger for a moment and play out how it sneaks up on a camp of bad guys and reports back to his master and things like that, instead of just roll and be done.