The closest matches on Steam are Five Nights at Freddy's 4, Five Nights at Freddy's: Sister Location, Five Nights at Freddy's 2, Five Nights at Freddy's 3 and Freddy Fazbear's Pizzeria Simulator.
From the Steam games with at least 2,000 reviews and 80% or more positive, we keep the ones whose main player tags match Ultimate Custom Night's most closely, then show the closest first.
