Where can I find something about them? I searched in the "help" section, but found nothing about it. One of the pets I bought has used a mutagen, when I look into "research potential" and I just wanted to know what are those

Mutagens are an item that randomly changes one of your pets genetic componants (this includes markings/coloring).And I mean randomly. Some people have great luck, some do not. It is random so you could be getting something good, or something bad. That is the joy and risk of mutagens.

You can buy them from the magic shop while exploring for 5k, find them in treasure chests, win them from beast temples, buy them from other users and bought from the state store for three gold coins.

I hope that helped :)

Yes, it helped! Thank You very much:)