When Pokemon first landed in the US, it was around the time Pokemon the First Movie was coming out in Japan, and there were screenshots online of Marrel, who did not yet have a name or was even in the game. Because of this all sorts of rumors and speculation popped up online all over the place, and of course people claimed that it was a secret, ultra-legendary pokemon that you could get in the game somehow. I remember being one of those people that briefly became obsessed with trying to get this mysterious pokemon which was popularly called Pika-Blue due to its similar appearance to Pikachu and that it was blue. Some of the methods for obtaining him were just outrageous, but there were actually people who tried lol. One method I remember was something alone the lines of you needing to catch every Pokemon (including Mew), maxing every pokemon's level out, and then surfing between Cinebar and Palet Town on an ultra specific route. I man on a island would appear and after talking to him, one of the barriers that separated you from the outside world would open up and there would be an island were you could catch Pikablue who was the most powerful pokemon in the game! I never tried it, but a few poor bastards did and were understandably pissed when it didn't work.
I remember similar rumors on how to catch Mew. At least with Mew he actually did exist within the game and there is actually a legit way of catching him.