Do they do anything? Or are they just personality things like treasure chests? I wasn't sure where to put this, but I figured since their only use was to be attached to pets this was a better place then most.

They exist to look pretty and to give funny names to. c:

I don't think they do anything.. I wonder if they help you out in the battle arena?

Nope, minions do not help in battle.

Some minions can be equipped as weapons. Not all, though

They stabilize your pets happines levels, and of course, they also look cute and can be given awesome names.