Continuity mistake: In the first episode of season 6, "Rebirth", near the end after the real Fry comes out of the Rebirth chamber, the robot Leela says that she and the robot Fry are in love she now has the real Leela's mechanical arm device on. But she never had it before or after that shot.
Continuity mistake: Season 6, episode 19 "Yo Leela Leela": When Bender discovers Leela's secret writing place, throughout the entire scene the lipstick marks on his head keep changing places, sometimes disappearing and reappearing. Most noticeable is the one on the right side of his head: it disappears when he is shown from that side, then reappears as soon as the angle changes.
Answer: You are thinking about episode 20 of series 2 - "Anthology of Interest I". She technically never kills anyone, but in the episode she ask a "What if machine" (one of the Professor's inventions) what would happen if she was more impulsive. The machine then shows the more impulsive Leela killing off the Professor to get the money from his will and thereafter killing Hermes, Bender, Scruffy, Cubert, Nibler, Amy and Zoidberg to cover it up. Finally she does something really impulsive with Fry.
Andreas[DK]