Bonus Episode: The last episode of the series aired was "Rock My World", which doesn't really have anything to do with the overall plot. However, it seems that the producers realized it would be the very last episode instead of "End Game" and threw in an Animation Bump, Awesome Music original to that episode, some light Fanservice by bringing back Holiday's little sister, and crafted the plot to be just 22 minutes of Rex being awesome to let the series end on a high note.
Keep Circulating the Tapes: Only the first 9 episodes have ever been released to DVD; thankfully, the entire series is on iTunes and Netflix.note This includes the Bonus Episode "Rock My World", in case you were wondering. However, there are 2 missing episodes from the "Season 2" batch for some reason on iTunes, leaving the series incomplete on that service. Not only that, but only the episodes in "Season 5" are available to buy in HD for some reason, when the entire series was produced in the format.
As of mid-2017, the two episodes are now available on iTunes. Still not HD, though.
Screwed by the Network: The back half of the final season went straight to iTunes, despite network promises that it would actually be aired. It did actually air... ten months later, where it was quickly shown over a few days in the morning, and is still missing two episodes.
Earlier character designs for Rex were much closer to that of the original M. Rex comic.
The series was originally going to share a world with Man of Actions other CN series, Ben 10, but toyline legali issues prevented this from coming to fruition and so the two did not share a universe, though the two series would eventually meet in a crossover.