In 2011 I drew a comic about two guys arguing over how Pokemon talk to each other. Shortly after I posted it, someone said they wanted the “Pewter City Gym” hoodie I drew one of the characters in.
Inspired, I proceeded to mess around with screen printing in my garage until I found a decent design. In total I designed shirts for three gyms: Vermillion, Fuschia, and Pewter City. Even now they remain pretty popular on Redbubble.
Most importantly, it had to look like a real gym shirt. This served two purposes: first it felt authentic and next, since most gyms printed their shirts on the cheap it meant I could sell these shirts for less. This was greatly appreciated by everyone, including the Pokemon subreddit I posted my first shirt to. They liked them so much I ran a few designs for the next shirt by them and let them vote on their favorite!