Marvel's Spider-Man Remastered is an exclusively single-player experience, as is its follow-up Spider-Man: Miles Morales, which is coming to PC soon. But it appears developer Insomniac Games toyed with the idea of multiplayer in its open-world superhero game, as suggested by information uncovered within the PC version's executable file.
The initial discovery was made by Twitter user DniweTamp, who posted two images showing lines of text purportedly from the game's executable. One image references a phrase "Superior Spider-Man", which can be applied to either Peter Parker or Miles Morales. Other lines make reference to red and blue teams, which alongside the phrase "Superior Spider-Man", imply that Insomniac was working on some form of competitive multiplayer mode for its game.
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That's not all. Another image includes what appear to be dev notes in the code, stating "If set and in co-op, Character 2 will see this text." This implies Insomniac also had a cooperative mode for Spidey in the works, letting players team up and battle thugs across New York together.
As for the validity of the images, gaming news website VGC stated in its own report that it had "verified the contents of these files, confirming these elements". So it appears the files are legitimate.
The most likely reason behind these hints toward multiplayer is simply that Insomniac tested out multiplayer functionality for Spider-Man, but decided to ditch it, either to reduce the scope of the project, or simply because the studio couldn't get multiplayer to work the way it wanted. That said, it's possible that this could also represent a test-bed for multiplayer in Marvel's Spider-Man 2. Insomniac has previously referred to the sequel as Peter and Miles' "most epic single-player adventure yet." But the game will feature both Spideys in its campaign, and allowing cooperative play would be a heck of a hook for a second game.
Either way, for the moment you'll have to content yourself with single-player Spidey. The good news is, that's by no means a poor alternative.