For several years, a fan theory/joke over the fate of Thalia to The Gitrog Monster stayed up thanks to a sketch comedy group.
Back in 2016, Magic: The Gathering first introduced us to the card The Gitrog Monster in Shadows Over Innistrad. A frog horror monster, the original card held one hell of a punch, costing five mana and being a big 6/6 creature with deathtouch and an affinity for land cards.
However, it soon became infamous for the art. The Canadian sketch comedy group LoadingReadyRun quickly made a big deal of the artwork, joking that the arm sticking out of the monster was actually Thalia's. It quickly became a running gag, but it also became something of a rumor too. Eventually, Magic had to come out and say that, no, the arm wasn't Thalia's.
Still, the rumors persisted, even though both characters were seen on subsequent cards. Finally, because sometimes Magic loves to address fan theories via card form and to put the whole matter to rest, March of the Machine finally had a card showing not only The Gitrog Monster, but Thalia riding it as well.
While this pretty much officially killed the theory, it also sort of killed the joke. Nonetheless, it solidified The Gitrog Monster's popularity, with it showing up in sets like Bloomburrow Commander and even appearing the the Thunder Junction storyline in only the next few years. A frog monster shouldn't have been this popular, but thanks to a constant joke and a never dying fan theory, the creature managed to stay alive.
The Gitrog Monster is also by no means the only one to have become so popular because of a fan theory. But it is one that has appeared multiple times in multiple planes in only the last few years too. Not many creatures can say that.
