This crippling mutation renders a mutant mentally weak and helpless! The Willpower of the mutant is reduced to 3.
Players and Mutant Lords might feel that this mutation as being too broad, and thus, way potent as a defect. A ML can rule that Weak Will only renders the mutant's mental defense down to a WIL of 3, while maintaining normal Willpower for everything else. This is reasonable, as this mutation is based on Gamma World's Mental Defenselessness.
Players who like to have the mutations reflect the character's personality could have the mutation make the character gullible, or a socially immodest — keeps nothing personal and never being embarrassed about oneself.
For androids and robots, they may lack any protective systems, leaving them prone to hacking.