In Urtuk: Desolation, you travel the land in an attempt to survive the ravaged world, encountering troublesome bandits, bounty hunters, grotesque monsters, and more. After a battle ends, you have the option to extract mutations from your enemies and use them on your party members to improve their attributes. You have to extract them after the fight and then decide how to use them.
When you complete a battle to extract these mutations, you need enough Life Essence to do so. If you don't have enough Life Essence, you won't be able to extract them from an enemy and you will have to move on to the next encounter. Usually at the end of a battle your party is given a decent amount of life essence, so extracting at least one mutation should be possible.
After extracting the mutations from the battle, you want to access the group menu located at the top right. Click here, then choose the group member to which you want to apply the mutation. Each party member can carry three different mutations and an ability to focus. These mutations have a notable quirk that improves character, and some of them have drawbacks. For example, a mutation can grant a character an unshakeable trait, making them immune to the abilities to push, pull, grab, or disparage enemies. However, this decreases their maximum health by a certain amount. You have to think about how many characters you want to place, because the more you put in, the more negative effects they take.
You unlock more mutator items by engaging creatures, helping wanderers you meet, and jumping in encounters. However, you don't want to extract enough of each mutation element. The more you acquire, the less life essence you have to use to extract the rarer ones.
