It's Been so Long Five Nights at Freddy's 2 Animation
The animation shows a story of a mother whose child went missing after leaving a restaurant and later committed suicide after discovering that a killer had disguised himself as a friendly animatronic (Golden Freddy) to kill the children who attended the party, and his child was one of them.
She later revealed herself to be Marionette, and when her friends and his child died, she dressed them up in all of the animatronics' costumes from the party in order to bring them back to life. A warning icon appears near the end and remains in the second frame before disappearing. At the end of the video, there is nothing but a black screen until the puppet appears with the FNAF 2.
NOTE: The following video contains a screamer!