We could implement a system similar to that brute thing on toribash, with a forum based game:
we buy our pet, then we challenge other users pets, max 20 fights a day. Fights would be like *Insert random, short and colorful flahs animation here*. Every win brings you 3tcs. Pet has his own qi and his avatar is shown ingame, avatar changes and gets cooler when pets belt up.
Also, it could be ogame-like: your pet can be challenged and win/loose even when you're not online, you can also attack pets of inactive members. Logs are sent via pm.


Edit: avwave, those pets are awesome