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In early cartridge revisions of B/W, defeating the E4 and returning to Route 1 allows the player to fight Green Cheren on Saturdays.
His party is identical to the repeatable Cheren fight, however he will always have Serperior regardless of the player's starter choice.
Unlike Cheren, Green Cheren is much more brash and outspoken. He was likely removed from later revisions of the game due to his post battle dialogue stating his intense hatred of the LGBT community.