He had not searched in the real world, because the barriers between universes were sturdier there. To search, he would have had to travel to that universe and activate the machine.
But the Dreamscape was different. All universes shared a common Dreamscape, where each universe's dream bubbles accumulated like a vast database. He chose to search there for the brainwaves he wanted.
During his experiments, he had encountered a problem: the viral frequencies used for brainwave contamination could not be fabricated out of thin air. The viruses he created were either unusable or uncontrollable.
In the end, he discovered that the most useful virus was himself.
More precisely, his brainwaves possessed an extremely unusual nature. They differed from Batman's and from Joker's, yet carried traits they both shared. For any Batman, this was a fatal contamination.
However, these brainwaves required a special carrier: his blood. It seemed that only blood fused from Batman and Joker could bear the combined brainwaves of both.
So he turned that blood and the brainwaves it carried into a special contaminant. Metal was the ideal solid medium for adhesion and transmission. As long as he deployed this metal into other universes and kept it in constant contact with Batman, they would be contaminated.
The wide-range brainwave search device invented from this principle worked similarly. Because it contained the brainwaves of both Batman and Joker, it could easily identify which brainwaves in a universe belonged to Batman and Joker.
It could therefore analyze the states of Batman and Joker in that universe, sort them into categories, select the useful ones, and include them in his plans.
During the search, he discovered a special individual. The other party possessed both Batman's brainwaves and Joker's, with an eighty percent similarity to his own. The only difference in that