Flexor is a Miles Mayhem mask, worn when he drives Buzzard, and it produces a flexible energy shield. The fan wiki lists five second-season episodes and notes that it looks the same as Deep Freeze, the mask his brother Maximus wears in the same vehicle, except that Flexor has a pinkish forehead and Deep Freeze a green one. Wikipedia’s character list and Matt-Trakker.com both list Flexor for Miles.
None of our Kenner toy records for Buzzard lists a Flexor or a Deep Freeze, so we cannot say which mask, if either, came in the box.
