A troll star is a star that can be obtained, but, won't raise your star counter. A troll star's appearance is identical to a normal stars appearance depending on the game they are in. They are usually indicators of where a nearby star is, even though Mario will have to trek back to this position to explore. The hidden star is usually in a very obscure spot, so the star may actually be helpful in that sense. In later hacks troll stars usually have a giveaway that they are fakes. Some are upside down, lopsided, or even have slight differences in appearance.