Tons of Sci-Fi and videogame references. Mordecai and Rigby are actually facing a threat to their friendship and even better, there is nobody to blame but them. A Rigby arc (the show doesn't do nearly as many for him than it does for Mordecai). A very good use of Pale Blue Eyes by The Velvet Underground. It's always funny when Muscle Man ends up nude. There are two very good instances of dark comedy when:
1. Mr. Ross kills future Mordecai in front of current and HS Mordecai, and the later, shocked, remarks "Dude, did we just... die?"
2. Rigby decapitates Mr. Ross and, thanks to his time collar, his head keeps reviving and dying while only being able to repeat "NOOOOO!"