Mutation

 is a gun that fires a slightly homing continuous beam with heavy recoil, leaving a trail of red liquid. Mutation also turns enemies red, though this is a purely cosmetic effect.

Trivia

 * The synergy between the Mutation and Bionic Leg/Shock Rounds may be a reference to Tetsuo from the 1982 manga series Akira. Tetsuo similarly possesses a bionic arm, and famously undergoes extreme and disturbing mutations. The synergy's name, "Neo Tech, Yo" also seems to allude to Neotokyo, the setting where the story takes place.
 * This gun may be a reference to the game Prototype, where the protagonist's mutated arm attacks in a similar fashion.
 * "Didn't Need Two Anyway" refers to the look of the weapon in-game, which envelops the player's whole arm.
 * This visual effect is also shared with Robot's Right Hand, Robot's Left Hand, and Megahand.