I am an inexperienced GM. I have minimal to none experience game-mastering, although I DO have some experience as a player, and I wanted to prepare a game for a great friend of mine who is a very experienced GM and that never has a chance to play because people expect him to be the GM all the time. Given that I'm both an inexperienced member and game-master, and also not a native english speaker, I'd like to apologize in advance and ask you people for whom my language may seem weird or my ideas downright silly some patience when reading or answering this question.
So I've started to think about plots and ideas and a setting for a campaign. I've given up on creating a new world because I've never done it before and I'm afraid I wouldn't be up to his standards on the cohesion of it. I've also thought using an already existing scenario would be a bad idea because he knows much more than I do about most of them so it would be very hard to bring him something new, or entertaining.
I've come across an idea: to use an already-existing scenario not related to any role-playing game that has a great setting but no plot advance and create a plot from there. Ridiculous as it seems, the MOBA league of legends seems to meet those requirements, and I am heavily thinking about starting a game using the Runeterra scenario. Although he could always research it, I don't think this friend of mine has ever played the game or remotely thought of it as a source of ideas for any game, so I'd at least be trying something new"
It raises a lot of questions, though, if this IS a viable idea. Are there any chances that this is a terrible option? Why? Any advice?