A Bicyclops Built for Two - S2-E13
Continuity mistake: When the professor hits the button on the keyboard to send them online with AOL there are some items on the table beside the keyboard. When it cuts the items are gone. (00:01:00)
A Bicyclops Built for Two - S2-E13
Continuity mistake: When Fry wants to go in the forbidden part of the planet, he jumps over the fence and fell in a trap, which is in grass. When he returns later, it is now a road. (00:13:15 - 00:17:20)
A Bicyclops Built for Two - S2-E13
Revealing mistake: At the end of the wooing near the end, you can see that Fry has four arms.
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]