I just used 5 mutagen on almost all normal Roc (with musical beak and electric gland green skills only):

Normal paws changed to Clumsy paws.
Normal senses changed to Deaf.
Normal senses changed to Deaf.
Normal muscles changed to Weak muscles.
Musical beak changed to Weak beak. 

Oh well. What's your story? Let me know how much luck/bad luck do you have with these kind of RNG :)

Mutagen almost always gives bad genes. It isnt really RNG (so praying to the RNG gods will not work, i've tried). It works on the power of the genes. Most bad genes hover around the 60-90 power, while most good genes are around 30-50, and normal is 70. A lot more likely to get a 90 than a 30. Which is why I now trade my mutagen away instead of using them myself. I always end up ruining some poor pet ... For science xD

Right now it's truly random. We had it depending on the gene power before while we were in beta phase. But the gene pool is designed that way that Mutagen was producing mostly "normal" genes and a few of those that are above them, so it was almost useless. Then the logic was updated to equal probability for all genes. It's easy to ruin a pet with it, but also easy to make small improvements and add something new to your own gene pool. Of course, it's not a precise instrument and it can't be used for fine tuning a precisely bred pet.

Really, huh. I thought it worked with the gene's power with how much bad luck I was getting. I must make more sacrifices to the RNG gods!

I just wish there was a way to choose only one row of the genes. Like use mutagen on jaws/brain/skin color etc. But then, that would probably ruin the game, it would be easier to feed pet with mutagen row after row till desired result appears and then move on, if player could afford enough mutagen. I really love that Explore offers the possibility of color change, at least.

It would be awesome if Viridian turned from a suggestion to reality, then mutagens would be used to make Viridian and not for ruining pets by accident.

I had a lovely Ocelot gryphon with all bad genes. I thought, "Well if she has all bad genes, then surely they can only get better!"

I used a Mutagen, and it changed her color. She is now a boring, typical colored gryphon with REALLY bad genes

D;