The Mutant template can be added to any creature. The mutant is not a traditional d20 template. There is no list of static features. The creature type does not change. The mutant template simply adds new elements to the existing creature.
Although mutant characters will gain extraordinary new abilities, they will also be subject to debilitating defects. The challenge rating or effective character level does not change, as the mutations and defects are designed to offset one another.
A mutant creature uses all the base creature’s statistics and special abilities except for those affected by mutations or defects.
A mutant creature retains all the special qualities of the base creatures and gains the following:
Mutations: The mutant creature gains three mutations.
Defects: The mutant creature gains three defects.
Medical Incompatibility: The mutant is changed and thus does not benefit as easily from medicines designed for the base creature. For example, a mutated human might not take well to a drug designed for normal humans. A mutant must make a Fortitude save (DC 15) or suffer a random effect from the Medical Incompatibility table. Some mutations and feats (such as the Super Mutant feat) modify this save.