Continuity mistake: When Fry is being emperor and Leela is questioning his actions, there is a water being with a yellow mouth cover. Later, there is a pink mouth cover on that being.
Love's Labors Lost in Space - S1-E4
Continuity mistake: In the scene around the table, Leela is holding a lilac coloured cup. This changes to a red coloured cup later in the scene. (00:04:05 - 00:05:10)
I, Roommate - S1-E3
Continuity mistake: When the TV first loses transmission and fills with static Fry taps it and it tunes back in, he then does his Fonz impression facing the sofa, it then cuts and he's facing the TV. (00:12:45)
I, Roommate - S1-E3
Continuity mistake: When Fry uses the ship engines to dry his hair, the Planet Express ship has rotated 90 degrees from the previous shots. (00:01:45)
Continuity mistake: In the scenes with the robot elders, the colour of the Elder's eyes change frequently between shots.
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]