MyPet-Premium is the paid version of MyPet that the author of MyPet offers on Spigot. It has additional features and new features will most likely end up in the premium version. All premium fetatures should be marked with a in this wiki to make it clear that the free version does not have them.
These are the current features that the premium version has over the free one:
If you purchased the premium version of the plugin you can select up to 2 Minecraft usernames (UUIDs) who will then get particle effects on their pets!
You can find planned premium features here.