Question: Sorry if this is off topic, but this seemed to be the best site to ask.

I can think of several examples of the use of a narrative technique: a last-second change in mood, often occurring so close to the end of the work that the audience cannot respond to it, potentially forcing them to reinterpret what they've experienced up to that point.

A plot twist that doesn't change the mood of the story (such as the reveal in *The Usual Suspects* or the "Wait, the monster isn't dead!" cliche in horror) is not an example of this, nor is a plot twist necessary for this to occur (The absolute best example of this I've been able to find is in [this short animation](https://www.youtube.com/watch?v=XMv5xMwdau4)) though one can be a catalyst (for example in the 'true' ending to the game [*The Witch's House*](https://www.youtube.com/watch?v=37FWMIPvN3g)). It is distinct from Bathos, though if applied properly Bathos could be an example of this. It is perhaps the same as or at least a narrative equivalent of a similar technique in music, for example in the opening theme for the game *The Legend of Zelda: Majora's Mask* (which also uses it to a degree in the opening cinematic it plays over) or with the more commonly used Picardy Third.

My apologies for the lack of links- my reputation doesn't allow posting more than two. I'll edit this once I can, until then it shouldn't be too hard to find what I'm talking about using google.

Answer: 
Consider simply calling it a **reversal**.

> 
> A reversal is when something (character, plot) appears to be one thing, or going on way, and changes on a dime so that there’s a perspective shift and the reader (and characters) see that thing differently.
>  [- What is Reversal in Fiction Writing? by Vicki Hinze](https://vickihinze.com/what-is-reversal-in-fiction-writing/)
> 
> 
> 

The ones you cite are specifically *character* reversals, revealed at the end of each narrative.

> 
> So in short, a character reversal is when we perceive a character in one way and then discover that character is different from our perception. He can be better than we thought, or worse than we thought, but he’s definitely different than we thought. And yet when we learn his true nature, it’s plausible for him (and thus to the other characters and readers).
>  [- ibid](https://vickihinze.com/what-is-reversal-in-fiction-writing/)
> 
> 
>
***Bathos*** is sometimes used more broadly to mean *any* sudden change in the tone of a work:

> 
> Bathos is a sudden change of tone in a work of writing, usually from the sublime to the ridiculous.
> 
> 
> [www.literarydevices.com](http://www.literarydevices.com/bathos/)
> 
> 
> 

In its broad sense it does cover what you want, although there is nothing in the definition which limits the device to the end of a work.

Unfortunately, neither Oxford Dictionaries nor Merriam-Webster list this broader definition.

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Alternatively, creators employing this method can be said to be ***[pulling the rug out from under](http://idioms.thefreedictionary.com/pull+the+rug+from+under)*** their audience. The phrase is used [here](https://www.tapatalk.com/topic/981879-mythic-scribes/17334-pulling-the-rug-out-from-under-the-audience).

Alternatively, you might call this an example of ***subverting (audience) expectations***.