Kara and Jimmy's mutual attraction reflects a similar flirtation between Supergirl and Jimmy in Silver Age comic books. That flirtation culminated in an "imaginary story" (the term used to describe a comics story that wasn't a part of the main comics' continuity) where Jimmy and Kara were married.
This is Aaron Ashmore's first episode since having a slot in the opening credits. He was not in Bizarro (2007) or Kara (2007).
Jimmy is frozen almost to death in this episode. Aaron Ashmore's twin brother Shawn Ashmore is known for his portrayal of Bobby Drake, the Iceman, in the X-Men films.
This is the first time to feature a Smallville Sheriff in the final cut since the death of Sheriff Nancy Adams in the Season 5's "Lockdown". Another Sheriff appeared in a filmed scene of the episode "Tomb", but that scene was cut before the final edit of that episode.
The episodes title, "Fierce", means to be hostile or violent in force. The title is probably cross-promotion for fellow CW show America's Next Top Model. Supermodel Tyra Banks, who hosts the show, frequently exhorts her models to be "fierce" as they battle through a modeling competition. Similarly, Kara and the other girls in the pageant are in a competition to win the Miss Sweet Corn crown. Tyler, one of the Weather girls, was played by the winner of the third season of America's Next Top Model: Eva Pigford. The title is most likely a reference to Kara's attitude and could also refer to "fierce winds", as Tempest had the power to control the wind.