The most challenging episode was either the musical or an upcoming Bat-Mite episode, but they were challenging for different reasons, so I'm having a hard time comparing. Right now I'll just say the Bat-Mite episode, but if the post continues to be as smooth as it's been so far, the musical could return to the top slot.

The most fun for me was "Legends of the Dark Mite", mostly because of the Great Piggy Bank Robbery homage sequence.