Rigor Motor is a hot rod shaped like a coffin or casket; its name is a play on "rigor mortis" (the stiffening of a dead body) and "motor". The shape of Rigor Motor's bubble canopy resembles the cockpit of the similarly coffin-based "DRAG-U-LA" show car, designed by Tom Daniel for the sitcom The Munsters.
In 2014, changes to the casting were apparently made, but there are no noticeable differences. In 2017, a major change to the casting was made, with the front bird ornament cast into the body, the skull ornaments removed, the canopy and engine made smaller and the base made plastic; these were ostensibly made for cost-cutting.