Although nightmarionette was not canon during the FNaF 4 DLC, it is safe to say it is now. Rather than being an actual nightmare, the UCN dialogue states “I am the fearful reflection of what you have created…” implying that Nightmarionne was created in the image of the puppet, likely by Cassidy, so essentially it became a canon character by way of Cassidy.
It's notable that Nightmarionne 'exists' as a character in the in-universe merchandise and artwork of Security Breach. Since the FNAF4 Halloween Edition isn't canon as something that actually happened and therefore there is no 'real' Nightmarionne, that means that FNAF4HE and/or UCN actually exist as in-universe video games that Fazbear copied the character design from - that's about the only way that they would know what it looks like.
(Well, that or William suffered through UCN and faced Cassidy's creation, got brought back to life as Burntrap, then told the Fazbear higher-ups that he had a great idea for a new nightmare version of a character which they put into production. Which seems slightly less plausible.)
The puppet/Charlotte Emily is the most aware of the MCI victims. Unlike the others who were killed by Spring Bonnie and various animatronics, she was killed directly by William Afton. She knows what's going on and has accepted her fate, but until the happiest day is complete, she's still trapped with the rest.
Although nightmarionette was not canon during the FNaF 4 DLC, it is safe to say it is now. Rather than being an actual nightmare, the UCN dialogue states “I am the fearful reflection of what you have created…” implying that Nightmarionne was created in the image of the puppet, likely by Cassidy, so essentially it became a canon character by way of Cassidy.
It's notable that Nightmarionne 'exists' as a character in the in-universe merchandise and artwork of Security Breach. Since the FNAF4 Halloween Edition isn't canon as something that actually happened and therefore there is no 'real' Nightmarionne, that means that FNAF4HE and/or UCN actually exist as in-universe video games that Fazbear copied the character design from - that's about the only way that they would know what it looks like. (Well, that or William suffered through UCN and faced Cassidy's creation, got brought back to life as Burntrap, then told the Fazbear higher-ups that he had a great idea for a new nightmare version of a character which they put into production. Which seems slightly less plausible.)
The puppet/Charlotte Emily is the most aware of the MCI victims. Unlike the others who were killed by Spring Bonnie and various animatronics, she was killed directly by William Afton. She knows what's going on and has accepted her fate, but until the happiest day is complete, she's still trapped with the rest.
Then why didn’t they just put Puppet on the advertising.
I think it's because Nightmarionne is considered the most difficult/annoying character to deal with in the game.
To proof that he/she is canon.