[Question] MIDIs, reinstrumentation, rearrangement and legality

I've been considering using MIDI reinstruments/remixes for my game, but i don't know much of the legal implications for it, both here and in general. I split my questions in two:

First
- Is it against forum rules to showcase a remix/rearrangement of a MIDI or any copyrighted pokemon song in the forums?
- How do the crediting works? Should i credit only the original composer or also the person who made the MIDI.
- If yes to the previous question, if the original MIDI does not have any way to track the person who made it, can it still be posted/used?

Second
- Besides the obvious crediting for the game (original composer, rearrangement) is there any problem with using the music in a non-profit game? Is that fair use?
- Is retitling an instrument shifted song taboo?

I'm fairly new to the forums, so I couldnt tell you much about your first question, but I think I can offer you some insight into the second question.

Invoking fair use requires you to fulfill four requirements: purpose, nature, amount, and effect. In general, nonprofit fulfills the purpose requirement, so long as you can make the argument that you're using it strictly for educational or criticism purposes. If you're using the MIDI in a non-pokemon game just for the sake of having it in your game, that's a nono. If it's in a pokemon-type game, you might be able to invoke criticism. Education is always a weird one, so I won't go into much detail there. Nature of the copyrighted work is kind of weird, primarily because I'm guessing your MIDIs were from published games. It's not super relevant to your concern, as this rule mostly deals with the dissemination of information and the like (things like factual statements are harder to copyright than creative works and so on). The last two are probably where you're going to have the most trouble. Amount concerns itself with just how much of the infringed work you're using. Essentially, the less you take, and the less important the stuff you take is, the better off you are. If you're using a miniscule clip or very short piece that really doesn't appear all that often, you might have a case if coupled with purpose.

Now, the fourth thing, effect, is where you might have a problem. Most people tend to assume they can invoke fair use because their game isn't making any money, and therefore isn't stealing from the infringed party. However, according to the law, this is simply untrue. Effect deals with how much your use of their product infringes on their potential market. In other words, if their music is being put toward a game that becomes a potential alternative for buyers (which it probably will be if it's free), you're almost guaranteed to fail a fair use case. Essentially, the less you use their work against them, the better off you are. If you want to use this piece in a psychology class to study how sea sponges react to video game music, it's hardly infringing on the creator's potential profits (sea sponges use a very different economic system from humans). If you're using a pokemon theme for a pokemon game being released to pokemon fans, you're practically asking to get sued, even if your project is nonprofit.

This is pretty much my fullest understanding of the things in play here. I might be wrong on some of this stuff, but basically, what I'm trying to say is, the non-profit argument is inadequate for invoking fair use.