Future Android 18

Future Android 18 is a much weaker, but more evil, alternate counterpart of Android 18 in the History Of Trunks and in the episode, Ghosts of Tommorrow.

Personality
In contrast to her main timeline self, Future Android 18 and her brother are extremely sociopathic and cruel, taking joy in killing and destruction. According to them, their personalities are the direct result of Future Dr. Gero's attempts at programming them to hate humans as part of his bid to conquer the world. Despite her brutal and cruel nature, Future 18 has shown instances of self-restraint, such as scolding her brother for murdering a clothing store salesperson despite intending to let him live.

Story
Six months after the Goku's tragic death in Age 766, Future Android 17 and Future Android 18 are released by Future Dr. Gero to kill Goku as part of his plot for revenge. According to Super Perfect Cell's flashback, Future Android 17 and Future Android 18 are willingly wandering through Dr. Gero's Laboratory as Future Dr. Gero is working on his "ultimate android creation". Future Android 18 knocks over some glass, Gero attempts to use his remote but Future Android 17 decapitates Gero. As Gero's decapitated head says that his "ultimate android creation" will absorb them, Future Android 18 blasts the head, as well as destroyed Cell's chamber in an attempt to destroy Cell himself. Then, the two androids head off to Amenbo Island, and they begin their reign of destruction.

Soon after, coming to the defense of the inhabitants, the Z Fighters challenge the ruthless killing machines. Future Android 18 kills Future Piccolo with a powerful kick to the abdomen, Future Tien Shinhan with a punch to his gut followed by a High-Pressure Energy Wave, and Future Yajirobe by breaking his katana before killing him with a High-Pressure Energy Wave too (this is a coincidence given the fact that Android 18 breaks Future Trunks' sword as well). The androids killed every single Z Fighter, including Vegeta and Piccolo. All in some thrill-seeking fun...