CostumeThe Dr. Muto costume that can be seen in one of the DVD extras movies was constructed by the Art Director, Steve "Scat" Caterson, and was also used for promotion at E3 2002. The actor in the video is the lead animator, Paul Metcalfe.
PrototypeIn the original internal proof-of-concept demo you start in the Doctor's lab, stop the power reactor from a total meltdown, and learn from AL that your lab mouse escaped during the chaos with the morph machine chip. You then needed to transform into a mouse yourself, travel through the walls of the lab and the colorfully decorated bathroom to retrieve the chip, and then return to the morph machine to power it up and enable the other not-yet-developed morphs. The sense of scale as a tiny mouse was very convincing.
At the time the collectibles consisted of batteries and not isotopes.