The Transformers Chocolate Flavored Cereal
The Transformers Chocolate Flavored Cereal would have been a chocolate-flavored concoction, not unlike Cocoa Puffs, manufactured by the Ralston Corporation. However, the cereal never made it to market and only test boxes have ever been found (one of which went for $349 on eBay).
The box claims the cereal would have had "more taste than meets the eye" and would have also had the ability to "transform ordinary milk into chocolate flavored milk" through some bizarre chemical process our weak human brains could never possibly comprehend. Continuing the "transformation" theme, the sides of the box would have had robotic limbs and a head drawn on them, encouraging kids to cut and fold the appendages a certain way to transform the cereal box into a robot.
There also would have been a mail-away offer for a Jazz toy. With the cereal never going to market, it seems likely that the Jazzes intended for this promotion instead became the ones given away via another Ralston cereal, Cookie Crisp, the same year.