The developers of the fan-made game “Mario Royale” had to hastily swap out a large part of the assets overnight. Did Nintendo threaten with a lawsuit?
What is Mario Royale? In the browser game Mario Royale up to 100 players can compete in a race against Bowser. Players could use items like the turtle shells or the star to knock their opponents out of the race.
What happened in Mario Royale? Almost overnight, Mario Royale received a new look and new music that are much cheaper than the originals. The new assets look as if they were quickly put together to replace the old ones, allowing the game to remain online.

While the developer does not explicitly say anywhere that they have received correspondence from Nintendo’s lawyers, their behavior suggests that it likely happened. The latest patch notes of the game state:
Shit. It happened. Please be patient while we fix the game over the next few days.
DMCA Patch
On the homepage of the game, it is now also referred to as “DMCA Royale.” However, it is still online and playable, even if it now looks significantly cheaper with the hastily cobbled together assets.
What are the reactions? Despite the short time that Mario Royale was playable, a small fan community has formed around the developer Inferno Plus.
I’m a sound engineer/designer, i’m good to do SFX for free dude.
— Magenta Iris (@MagentaIris) June 21, 2019
Some users on Twitter have offered their help to the developer, such as in creating new sprites or music for their Royale game. Most users there find the changes to the assets unfortunate, although not surprising.
It is likely that Nintendo would indeed have involved their lawyers at this point. In the past, this has happened several times, as in the case of Pokémon Uranium.