Fresh from the Cataclysm beta comes news of possible new combat companions. The Blue and Gold Mini Jousters, which were previously pictured as solitary birds, are in fact condors carrying lance-wielding rag dolls. These pets can be learned and summoned like any other companion, but (for the time being, anyway) they can aggro, attack, and damage mobs. Mobs can attack them back and even "kill" them, though they can simply be resummoned as good as new.
We already have vanity pets that can fight each other, such as Warbots, Clockwork Rocket Bots, and Grunty and the Zergling. And there are pets like the Toxic Wasteling, Willy, and Lil' K.T. who can kill critters. But so far all vanity pets have been 'non-combat' — they cannot help you fight other mobs. So it comes as quite a shock that the Mini Jousters seem to buck this trend. They are level 80 with nearly 31k hp and they can hit other mobs of their level for over 900 dmg per swing. You can even heal them up if their health drops. We're guessing their unique ability to attack mobs is a bug.
Another possible bug: they currently do not fly behind players on flying mounts. Instead, they will follow along the ground, where they can aggro hostile mobs.
We would not be at all surprised if the Mini Jousters' mechanics were changed so they could only fight each other. But in the highly unlikely event that they remain 'combat' companions, we can all expect to see a lot of them flying around Azeroth in December!