The Malaprop Diamond is a diamond appearing in the Rhino-Man episode of the 1987-1996 series. In the episode, J. Gordon Hungerdunger sponsors a superhero contest, in which the winner would receive the diamond. Krang also wants it, to focus a heat ray strong enough to break the Technodrome free from the Volcanic Asteroid. Thus, he entered Rocksteady and Bebop into the competition.
Unfortunately for Krang, the Malaprop Diamond is not an actual diamond, but a glass beaker containing the antidote to Hungerdunger's brainwashing fluid. Donatello empties the antidote into a vase during a final battle with Shredder, and tosses the beaker to Shredder. The heat ray malfunctions and explodes due to the lack of a true diamond.