The Farnsworth Paradox - S5-E10
Continuity mistake: In the very beginning scene, where Fry and Leela are talking, there is an explosion. When some ceiling falls down there is one big bit and three small bits next to Leela's foot but then a few seconds later there is one big bit and a few small bits all in different places. (00:00:40)
The Farnsworth Paradox - S5-E10
Continuity mistake: When Leela looks in the box, the wall behind her is red, then blue when it cuts back, then red again, and finally blue as she enters the other universe. (00:05:10)
The Farnsworth Paradox - S5-E10
Continuity mistake: When Fry first takes the tangled Christmas lights out of the fake box, they are all red and blue. However, when the shot cuts outward to get a wider view, many of the lights have turned green.
The Farnsworth Paradox - S5-E10
Continuity mistake: Just as Hermes A is about to shoot the box into the sun, all the crew (A and B) shoot out into the airlock. However, Hermes B doesn't come out of the box and just appears in the pile. This is confirmed in the commentary.
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]