: Barry Allen and Bruce Wayne team up to investigate a blood-stained smiley face button found in the Batcave.

In more recent stories (2025), The Flash #21 has explored even weirder cosmic horror.

In the world of DC Comics, "The Flash #21" has been the title of several major turning points across different eras. Whether you’re looking at the iconic "The Button" crossover or the first meeting between two generations of speedsters, these issues are legendary for redefining what it means to be the Fastest Man Alive. The Button: A Collision of Worlds