Anti-Serum

Rat Boy releasing the Anti-Serum vials from their secure display case. (COMIC: Jenny Everywhere vs. the Drag-Racing Monkeys)

In one universe, Anti-Serum was a substance of which the Master of the Drag-Racing Monkeys kept some vials in a safe display case in his laboratory. If a Drag-Racing Monkey consumed this substance, it would reverse the genetic engineering done by the Master on his “children”, turning them back into ordinary chimpanzees.

After stealing the vials from the Master's laboratory, Rat Boy tricked the Drag-Racing Monkeys into consuming them by pretending they were special vitamins, thus defeating the threat the Monkeys presented to the rabbits' city. The Master's memories were subsequently erased, making sure he could create no more Drag-Racing Monkeys. (COMIC: Jenny Everywhere vs. the Drag-Racing Monkeys)