The term SCI-FI BADDIE can be summarized as a villain from science fiction, and the crossword solution for this term is MUTANT, which has 6 letters. A MUTANT is a creature or organism that has undergone a genetic mutation, which is a change in its DNA sequence that results in a different set of characteristics than those of its parents. Mutants are often portrayed as villains in science fiction, due to their unnatural abilities and unpredictable behavior.