Series 2, Episode 14
Alex Cranz on Io9 put it best when they said: "I once read a 40000 word Buffy and Angel and Highlander and X-Files crossover with a self-insert lead character who magically woos Buffy and is super rich and best friends with everyone and super good at fighting and stuff and it was more believable than the nonsense Supergirl has delivered its audience with Mon-El."
I recommend reading the entire article, both because it's entertainingly written, and because it highlights one of the big problems with Mon-El's character: He's a Mary-Sue, through and through. A particular bad example of a Mary-Sue, and a particularly baffling one -- why is he in this show? I could hazard a guess, but I'm not sure I would be correct. My guess is that the CW, shy of the idea of a series not aimed at least somewhat at young men, insisted upon his presence to make the story more palatable to young men.
Maybe I'm completely wrong there. Maybe I'm not. Still, having talked about Mon-El as a character -- an unavoidable conversation, because for all that this episode purports to be about Jeremiah, Kara, and Alex, it is absolutely about Mon-El -- I'd like to talk about his relationship with Kara as shown in this episode.