Mutation is a primary gameplay component of Biomutant. You are able to dramatically change your genetic structure to adjust your appearance, gender, attributes, and abilities to better match how you want to play. It is impossible to mutate to a completely different type of animal such as a reptilian creature. 
Mutations can be caused by Bio-contamination pools in the New World or radioactivity in the old world, and presumably unlocked by using bio points. There are multiple types of mutations. PSI-Mutations only give abilities such as telekinesis and levitation. Biomutations add body parts such as crab claws which allow you to pinch people, then throw them somewhere, or slam them into the ground, or barbed tails. Bionic Enhancements add robotic parts to your character.