Can board game mechanics be copyrighted?

Board game mechanics (the process for playing the game) are patentable. Copyright does not protect the idea for a game, its name or title, or the method or methods for playing it. Nor does copyright protect any idea, system, method, device, or trademark material involved in developing, merchandising, or playing a game.

Is it legal to make fan games?

Yes you can create a fan game for free. Yes – you will be violating copyright and probably trademark if you use the soundtrack and assets from the show. If the creation stands on its own – the number of downloads won’t be directly linked to the IP which the content is originally from.

Are fan made games illegal?

Long story short: Any game which infringes either copyright or registered trademarks is illegal. Fan games using the names/world/sprites/story etc etc (i.e. are sufficiently like the original to be recognised as a fan game) will be infringing one or both of those. Therefore fan games are illegal.

Is Mugen legal?

The MUGEN exe license explicitly prohibits commercial distribution. As for characters ripped off commercial characters, they are legal as long as they stay in the fair use domain. However commercial use of original characters is fine so long as they’re no bundled with MUGEN exe.