'I just realized I'm not playing Spider-Man, ' he captioned the video.
Brazil's CCXP18 is unveiling some fresh looks at much-anticipated new superhero movies, which includes a major new costume for Spider-Man: Far From Home.
The actor continued to fuel rumors he would be playing the comic book baddie when he was spotted over the summer in London, where the movie is being filmed.
Are you a fan of the new looks? Photos from the set snapped backed in September showed Gyllenhaal dressed in a very elaborate looking get-up (sadly sans fishbowl), and rumours that the iconic villain would be the one squaring up against Spidey in the upcoming sequel have been swirling for a while now.
It's good fun, and a sign that we can expect the marketing for Spider-Man: Far From Home to start ramping up.
The film will see Tom Holland return to play Spider-Man and Zendaya as Michelle Jones.
This may be a playful nod to that brief period in 2003 when Tobey Maguire was trying to get a bigger payday for Sam Raimi's Spider-Man 2, and Sony called his bluff to the point where the studio actually met with Gyllenhaal as a possible replacement.
In the comics, Mysterio is the alternate name of Quentin Beck, a movie stuntman and special-effects wizard who uses his skills in creating illusions to commit crimes.