It looks like this was the case with Roblox’s Pokemon Brick Bronze, which touched on a franchise you may know. Brick Bronze was whipped up by a passel of player developers and enjoyed a very strong following (strong enough, in fact, that the game inspired its own wiki).
Nintendo might have gotten wind of the project, hoever, because Pokemon Brick Bronze was taken down on April 18th to be reviewed and quite possibly shuttered forever by the team at Roblox. To make this situation even stickier, there was money involved, and many players are demanding refunds spent on Brick Bronze.
Brick Bronze had a huge following, with tens of thousands of players logging in to enjoy the free Pokemon MMO.