Plushies are small achievements for the player in fnaf. There are different kinds of plushies like Foxy,Chica,Bonnie, and Freddy. In the first game you can buy Bonnie, Chica and Freddy plushies for 99 cents each in the android version. Oddly enough in the first game Foxy and Golden Freddy do not have their own plushie.
In the second game you can get plushies by completeing challenges on the custom night.