Nintendo has a history of being a bit catty with the likes of game modders and fan creations, having slapped down fantastic standalone games like Pokémon Uranium with cease and desist letters. It's perhaps no surprise then, that Nintendo has also taken a dislike to a new FPS game set in the Pokémon universe created by a single creator.
Yes they used a bunch of assets, but the game is just a private creation with some quick video made by the modder behind it for fun. It's nothing commercial, but Nintendo doesnt' care. Not only is it try to get the creator to stop making the game, it's trying to remove all video or images of the game from the internet.
Nintendo, enjoy the Streisand effect
Not sure how I feel about seeing someone shoot cute Pokemon in the face, but then again, if giant monsters were trying to electrocute me or set me on fire, I might want a sidearm handy when I went for a stroll in the woods too.