Hi, I may be able to help out if the project is of smaller scale. Im fairly competent at pixel art if that interests you.
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Not any vivid or revolutionary concepts for a multiplayer game, but a few basic ideas that could be built on.
Firstly, it shouldn't rely on a large player count as it it a challenge for indie games to get a large player count. So small, lobby based games in theory would be much more successful.
If you want something more feasible for a hobby project, it would be a good idea to look at existing sports as the rules are usually simple. Gimmicks and flair can be added to shake things up.
(The idea of some goofy wizards playing hockey particularly appeals to me)
It would also be neat to look at a small 4-8 player party game. Perhaps a fast paced rougelike where you and your friends fight to be the last one standing. However you cant directly kill each other, instead using the enemies/environment to do the job.
Im also attached to any ideas to feel free to critique or put a different spin on them.