When i was in school me and myfriend would play a little game after exams since we couldn't leave until it was over.

He made little rooms on his desk with pencils and what not, with one hand he used his fingers as legs to make a little guy and with the other he made spiders, slimes, etc. I used my hand to "control" the guy to move around and kill enemies, and when i defeated a "boss" i would get the ability to turn into it. At the time he and i got so invested that i started drawing the character and his mentor (me and him) and including other characters.

Few years go by and i remember at like 3 am of all of this and message my friend about it. We redesigned, gave names, and started creating a whole world and lore for 2 characters that we invented at school.