What are the actual YT laws regarding monetization of piano music?

[Pianist Da Sootopolis]

I have a YT channel with little content right now, mostly due to my laziness and due to time constraints. Hopefully soon I can get to uploading more! XD
Anyways, what are the actual laws regarding monetization? I've heard that, since most classical music is in public domain, you can make money off of just about anything classical (except perhaps Rachmaninoff, 75 years haven't passed since his death), but with game music that likely isn't so, since not only is it not in public domain, Nintendo probably has copyright protection up the butt (as they should).
So what're the actual laws (for the US)?

[MaestroUGC]

Welcome to that wonderful grey area known as "Fair Use". Generally, I've found that most publishers don't really care about this sort of thing, as many other channels cater exclusively to this style of content and seem to do alright with it. There might be a few exceptions, but generally you shouldn't be concerned with something like this.

Most publishers are more concerned with using, and abusing, their full games proper for profit, and just using individual assets (especially music) isn't a primary legal concern for them. Though that's generally due to how music is regarded in terms of other larger art forms; ancillary to the final product.

Though if you're really that concerned it'd probably be best not to monetize in the first place. All it takes is for one person to take exception to using their work in any capacity and then you're finished.