The Super Mario Mash-Up pack has been a huge success for both Mojang and Nintendo, as long-time Minecraft fans get to experience some of their favorite Nintendo characters in the game. That enthusiasm bled over into YouTube where fans were eager to showcase their creations, but some have been subject to copyright strikes against their accounts for uploading this content.
Developer 4JStudios is responsible for the Minecraft Wii U port and according to them, Nintendo assured them that copyright strikes wouldn’t happen on content uploaded to YouTube, so the development team is investigating.
We're hearing reports of copyright strikes on Super Mario Mash-Up videos. We were assured this wouldn't happen. Following up with Nintendo.
— 4J Studios (@4JStudios) May 19, 2016
Hopefully, this will be worked out shortly for those affected by the copyright strikes, as it can put a severe hamper on how well a YouTube channel does.