The stunt was part of a long-running joke about how Kimmel doesn't like Damon and always bumps him from his talk show due to time constraints.
After Kimmel unbuttoned Affleck's cloak and a sweaty Damon emerged, Kimmel admonished Affleck and tried to exclude Damon from their conversation, then cut Damon out of the camera frame before ordering his staff to drag his chair away.
Kimmel and Affleck then introduced footage supposedly cut from Batman v. Superman: Dawn of Justice, showing Kimmel revealing the secret superhero identities of Bruce Wayne and Clark Kent, who were played by Affleck and Henry Cavill. Also making a cameo in the clip was Jesse Eisenberg as Lex Luthor.
The segment ends with Cavill's character hurling Kimmel into space, causing him to land on Mars where he meets Mark Watney, the astronaut Damon played for his Oscar-nominated turn in The Martian.
"Now that you're here, I was thinking maybe we could do a talk show. You could host it and I'll be your guest -- every night," Damon's Watney said.
"Oh, yeah, no, no. I'm going to pass on that," Kimmel replied. "Congratulations on not winning the Oscar. I'm just going to go over there and die alone."