Somebody at Nintendo has apparently just discovered the existence of the Steam Workshop, and the Garry's Mod devs are now scrambling to moderate 20 years worth of user uploads to make sure they're free of IP violations.
"Some of you may have noticed that certain Nintendo related workshop items have recently been taken down," the devs say in a Steam news post. "This is not a mistake, the takedowns came from Nintendo. Honestly, this is fair enough. This is Nintendo's content and what they allow and don't allow is up to them. They don't want you playing with that stuff in Garry's Mod - that's their decision, we have to respect that and take down as much as we can."
It seems it's quite a job, too, as the devs note "we have 20 years of uploads to go through. If you want to help us by deleting your Nintendo related uploads and never uploading them again, that would help us a lot."
I couldn't possibly begin to guess the full breadth of Nintendo-related add-ons people have uploaded for Gary's Mod, but a quick search for "Mario" on the Steam Workshop returns 5,624 results across 188 pages, and that's just one corner of Nintendo's IP library. Godspeed to the devs now forced to sort through all this.
Nintendo has famously been extremely protective of its IP, but its lawyers have seemed extra busy over the past year or two. There was the takedown of images for emulators, the death of the Zelda: Breath of the Wild multiplayer mod, and the lawsuit that killed Switch emulator Yuzu. With each new creation from the Nintendo fandom, we just have to keep hoping that Nintendo itself doesn't actually take notice of it.