FNITC 3 is a sequel to 1 and 2, with mechanics from both.
Mario reappears as the protagonist yet again, determined to save the inhabitants of the Mushroom Kingdom from an angry Imp's evil desires.
Black Magic Wario
Wario makes his debut in this game as the primary antagonist. After being controlled by an Imp from another dimension, Wario brings Luigi back to life (again), and pulls Shadow Mario from the Dream World. He appears in the TV, paintings, and windows. You must flash a light on whichever he appears in to stop him from attacking you.
Shadow Mario, the primary antagonist of the first game and night 6 of the second game, takes a backseat as a secondary villain. After FNITC 1 he was trapped in the Dream World, but Wario, possessed by an evil Imp, returns him to the Mushroom Kingdom. He attacks you through the two doors, which you must regularly watch to keep him at bay.
Undead Luigi is Mario's brother, who has been zombified twice as of this game. He attacks you by wandering around the house. If you can hear his footsteps, hide under your bed. If you hear thumping it is safe to leave, but if you see eyes you must leave or he will kill you.
Melted Gold Mario
Not featured in the teasers, Gold Mario returns partially melted. He attacks at random, and there is no way to counter him, similarly to FNAF 1 Golden Freddy. When you are looking for Wario in a painting/TV/window, there is a very small chance that he will jump out of whatever it is you shine your light on.
You can hide under it to escape Undead Luigi
You can shine it on items to see if BM Wario is in them
You can use them to see Shadow Mario and stop him
-Wario's initials are BMW