Dee Dee

Dee Dee is a humanoid character similar to BB and JJ who first debuted in FNaF World.

FNaF World
First seen in this game, she's a NPC who only appears in the first area of the game, Fazbear Hills, walking up to her will start the "Dee Dee's Fishing Hole" mini-game.

To win the game, the player must drop their plunger to try and catch either one of the fish, or the pearl at the bottom of the screen. Managing to catch the pearl 5 times will reward you with a special pearl byte, which will heal your party during battles.

Ultimate Custom Night
On May 30, 2018, Scott Cawthon made a post on voices.com, describing a character simply referred to as "Annoying Girl" who was set to appear in the upcoming expansion to Five Nights at Freddy's 6 (which ended up becoming its own game), the character was later revealed to be Dee Dee on June 7, 2018, when a picture was put up on scottgames.com revealing her identity and mechanic. In this game, she's character who can randomly appear during the night, she will sing a short song then either add a new enemy to your night (either one from the regular roster or one of the secret characters) or increase the A.I. of an already selected one. She can be prevented from appearing with the DD Repel power-up.

A black-and-white version of her can appear extremely rarely during regular nights, or automatically in 50/20 mode. She's referred to as XOR in the audio files, and Scott Cawthon confirmed that to be her name during an interview. Whenever she appears, she summons all of the secret characters into the night, which include RXQ, Plushtrap, Nightmare Chica, Bonnet, Minireena and Lolbit.

Trivia

 * Her name was originally spelt "DeeDee", without a space. That changed in UCN.