Batman encounters the Creeper while on patrol and then investigates the Dr. Yatz case, discovering in the process that this new yellow-skinned vigilante is really Jack Ryder. Ryder and the Creeper learn that Yatz secretly intended the smart-skin to be a weapon and that tests on human subjects repeatedly resulted in mutated monsters. To achieve better results, Yatz took on a silent partner who introduced his own chemical "nerve agent" to the smart-skin, which resulted in Ryder's unique transformation into the Creeper. The silent partner is revealed to be the Joker and the "nerve" agent used was a version of his Joker venom, known to normally alter skin and hair color in victims while inducing temporary madness and uncontrollable laughter before killing them. In exchange for helping Yatz improve his results, the Joker wants to use the man's technology to create an army of maniacal, super-strong, near-invincible soldiers. Seeing the successful results with Ryder, the Joker refers to the Creeper as "family." A similar batch of smart-skin is then used to turn dozens of others into maddened, yellow-skinned soldiers with green and red hair.