Nathan Fillion really did have cameo in Guardians of the Galaxy Vol. 2, but it never made it out of the edit bay alive. Those who kept an eye on spy photos from the set were in the know, but now director James Gunn has enlightened everyone. Nathan Fillion was Simon Williams, a.k.a. Wonder Man, in poster form.
As fans saw in the film, part of the story takes place in St. Charles, Missouri. One part of that sequence, which was filmed but not shown, featured a movie theater hosting a Simon Williams film festival. The theater was adorned with one-sheets from Williams’ filmography including a Tony Stark biopic. Gunn shared that poster and details from the cameo on his Facebook page.