The Defenders Issue 109

Grant Gordon had a poster in his childhood bedroom that depicted the cover of an issue of Marvel Comics' The Defenders.

It had the tagline "Valkyrie's vengeance!", and featured depictions of Spider-Man, Doctor Strange, Valkyrie, and another character. (TV: The Return of Doctor Mysterio)

Behind the scenes
The issue was not explicitly identified in The Return of Doctor Mysterio.