10. Pokémon Uranium
Nintendo has a history of being spoilsports. They have frequently flagged Let's Plays as copyright and refused television programmes the rights to showcase their games; their biggest acts of misery, however, are - perhaps understandably - the curbing of unofficial third-party license uses.
Pokémon has always been a common culprit, both in gaming and beyond - in 2014, an artisan plant pot charmingly inspired by Bulbasaur was forced to stop production, to the disappointment of both its designer and practitioners of horticulture. The creator of Pokémon Prism, a ROM hack of Crystal, claimed to have received a cease-and-desist order just months before its December 2016 release, following eight years of work.
One of the most ambitious unofficial projects was Pokémon Uranium, created entirely within RPG Maker XP and released in August 2016. It featured an original score and storyline, complete with 200 species of Pokémon, 150 of which were original designs. Among these was an exclusive "Nuclear" type, created by an accident central to the game's events.
Sadly, the developer deleted all links to the download of this impressive creation, following numerous DMCA letters from angry lawyers. Presumably, Nintendo was annoyed that somebody had created a game better than many of their own Poké-offerings.
Official development was promptly discontinued, but not before Uranium had garnered over one and a half million downloads. Thankfully, community-driven updates kept the game alive for those who were lucky (or mischievous) enough to own a copy, with the most recent patch being October 2018, over two years after its lamentably short-lived release.