Spawn/Batman

Spawn/Batman is a 1994 one-shot comic book written by Frank Miller with art by Todd McFarlane and published jointly by DC Comics and Image Comics. The comic is an intercompany crossover between Batman and Spawn.

Plot summary
Batman comes to New York City in his search for an arsenal of high-tech weapons and robots that use decapitated human heads as their brains. Antagonistic, confrontational and suspicious of each other, Spawn and Batman engage in violent battles before realizing they are both after the same villain. Grudgingly, they decide to work together. The person they seek has been kidnapping and decapitating the homeless for use in the robots, but that’s only part of the plan: There is also a nuclear arsenal ready to be deployed.

Continuity
A note inside the front cover states that the one-shot is "a companion piece to DC Comics' The Dark Knight Returns. It does not represent current DC Comics continuity." Though the crossover has never been a part of the ongoing Spawn continuity either, it is a commonly held belief that the scar appearing on Spawn's face at the beginning of Spawn #21 is the same wound inflicted by Batman with a carefully thrown Batarang at the closing of the crossover, which is upheld by Spawn's remark in that very same issue that the scar was a result of his run in with "some bozo in black." However, through some slight retcon, specifically with the non-chronological release of issues Spawn #19 and #20, the "bozo in black" in question is actually revealed/changed to be Harry Houdini, and the scar in question is the result of gunfire that Spawn suffered while protecting Terry Fitzgerald.

Batman-Spawn:War Devil
Another meeting of the two characters was Batman-Spawn:War Devil published by DC. It was written by Doug Moench, Chuck Dixon, and Alan Grant and drawn by Klaus Janson.