I am not a lawyer, this is not legal advice, just my 2 cents.
So the composition "Epic Mickey" is originally by Thomas. Recorded 2018 in Cologne. The composition itself has nothing to do with Disney. I would have to ask Thomas, but I think he was only inspired by the computer game and therefore gave the composition the title. Only the title of the song is a direct reference, his music refers at maximum stylistically to that from Epic Mickey. And as far as I know, it is no violation of copyright law to deal with a topic artistically and to refer to it in the title.
He could have named it "Epic journey of a mouse", that would have been legal imho. To me it looks like he picked the term to associate his work with the intellectual property of Disney. The soundcloud page could be seen as part of his professional porfolio/advertisement, making it a commercial use, even if he makes no money from it directly. And "Epic Mickey" was filed as a trademark - at least for a time. Add to that the image of Mickey Mouse it makes it clear that he didn't pick the title by coincidence. It is my impression that trademark law exists to prevent exactly this kind of behaviour. Afaik in the US trademark law there are legal incentives to actively defend your trademark against infringements or you risk losing it. And I don't see how he could claim fair use on this. Also fair use isn't a right, it's a defense, it doesn't prevent you from getting sued, it's something you use to minimize damage after being sued, but once you're in a legal battle you're already paying a price. I would advise against doing stuff like this. In reality many things are legally not clear cut and will need to be decided by a judge, but I would always err on the side of caution with these things.
There was a case where someone got sued for throwing a Pokemon themed party:
FOLLOW-UP: Pokémon’s lawsuit to block fan party came without warning — or profitsThe Pokémon Company International, Inc. filed suit against two
www.geekwire.com
Regarding the use of the image of mickey, which I think falls under copyright law, not trademark law, as far as I can tell... I think that's just illegal, both in Germany and the US. You can't just take someone else's creation and use it for your own purpose, the same way others can't just take your music and use it however they want.
I really don't want to be a dick here, but it irritates me to see composers just taking pictures to advertise their music with, when clearly they don't have the rights to those pictures. It's not even a rare occurrence. But I hope over time it will get rarer and there will be more of a consensus of "you can't just do that" among musicians. There are many many images on the web that are under permissive licenses that allow you to just use them (whether you can be sure the original creators released them under that license is another story).
The copyright infringment I'm talking about is that someone downloaded his Soundcloud music, for example the track "Epic Mickey" and distributed it illegaly without any permission under an alias. And it's not just his music that got violated, it's the music of many others. The albums you can access via YouTube Music are compilation of music that has been stolen from different composers on Soundcloud.
That's both illegal and morrally corrupt on many levels imo. I'm really sorry it happened to him and others!
A while ago there was a musician who released some old demo tape of his for free on youtube and then the same happened to him and someone registered the work as their own. Absolute scumbag move.
I was planning to make a blackmetal album one day and when trying to figure out a way through the maze of German tax laws I was at the point where I thought "ah, fuck it, no one's gonna buy it anyway, might just as well throw it online for free". But then I thought about how pissed off I would be when someone else registers it in their name. It's not even about the money, it would just feel like such a violation and injustice, I'd take it personal. I wouldn't do that with the album being pirated, that's inevitable (or rather if no one cares enough to pirate it, I'd probably take that personal in another way). So I genuinely do symphathize a lot with all that have been affected by this already!
I think it's good that you made the thread and helped get the info out there, so that people have this on their radar and can make informed decision about how they release their music in the future.
Sadly I can't think of a satisfactory immediate solution to that problem though :(.