Synopsis

What would happen if Saitama became Jokerized?

When the Joker appears and wreaks havoc in the One Punch Man universe, Saitama springs into action and easily defeats the clown prince of Gotham, but not before the laughing villain manages to spray him with a peculiar gas. With his dying breath, the Joker uses the same device that he used to enter Saitama's world to teleport them back to Gotham city, where the caped baldy struggles to get his bearings on the alternate Earth, all while the strange concoction that he was hit with begins to transform him into something truly horrifying.