Pets: Do some pets help you in battle?

I noticed when looking at pet descriptions that not all of them mention that the pets don't participate in battle. Does this mean that some of them help you out?

If some pets do, it'd be nice if the preview videos showed how they help you out. Like if the fiery lizard helps light up caves, if the scorpion helps you fight, and so on.

All Pets are cosmetic only.

I really wish their descriptions would all say that then. Or have a disclaimer at the top of the pet store page instead of adding it to every pet. Something.