You need to enhance 5 different skills with mutagens that you
- loot from defeated enemies
- or create as a side effect of alchemy
The best quality is "Greater" and I recommend to fill only this ones in because all choices here are permanent.
The skills you can enhance are:
Training Tree
Arrow Redirection and Fortitude
Swormanship
Invincible, Combat Acumen and Whirlwind
Magic
Enhanced Yrden Sign, Sense of Magic and Control over the Power
Alchemy
Condensation, Metathesis, Berserker, Mutant and Amplification
This skills must be unlocked through skillpoints, after that go in meditation mode, choose "Character" and press Y at the skills you want to enhance by mutations. With the 5th one your achievement unlocks.