Mutants are humans and animals that have mutanted into more deadly Lifeforms. All mutants are hostile and when you are digging up a very big building, there is a possible chance of mutants coming out. If mutants do come out they will murder all your colonists then proceed to attack your buildings. In abanonded colonys and in the wastelands. Mutants reside and infest buildings to... what do they do with the buildings? make more mutants?
In Chapter 10, mutants are fighting back when you attack them. not only do they have the normal tower defenses but they also have a kind of Spawner defense that makes mutant units appear and attack your units.
To view all mutant buildings go here ----> Mutant buildings