There comes a time in every where the DM gets fed up with his players reading the monster manual and comes up with his own monsters. My monsters were of course much more creative than a bunny with fangs, bird wings, and antlers. For example the monster that could only be described as a chain chomp head on a giant frog body. That's way more creative than combining real animals into an amalgamated mess. Another astounding creation I created was the crazy metallic imps that shot electricity from their eyes and used their decidedly malleable structure to entangle the players with razor whip claw fingers. All in all I'm entirely impressed with my ability to construct new creatures.
Despite my over qualification in the creating creatures department, I'd still love to hear about the wacky and awesome monsters you've either unleashed on your players or have had unleashed upon you. Drop a comment with your story.
Image source GIS for jackalope