I love a good plot twist.
For a mystery I would (and still use) a red herring that still have some value to the story to keep the reader away from the big picture at first, then bring them to that ending where they go…“Oh… it was this other guys this whole time?”
I like a story that simmer some clues along the story. Clues that the writer will put all together at the end for the reader to go like Oh, so that is why the antagonist did this at the beginning or that is why they had that type of behavior or reaction to that question and so on.
Don’t just use the red herring just to lure the reader away, like in my WIP the red herring has a close connection to the antagonist and the reader only finds out near the end of the story.
I also like twists that are hidden in plain sight which is when the reader will interact with an NPC or even antagonist at an early stage of the story and during that conversation something will be revealed to the reader but it sounds banal or without value at this exact time. And by the end of the story the reader would go… “Oh… Crap!” lol
Which is why in mystery stories trust no one lol.
In a IF you can make it so that if the reader doesn’t collect all the clues, they miss out on some of the antagonist’s motive or even add collecting all the clues as an achievement (which can booster replayability for readers that goes for achievements)
It’s not easy to do because the writer need to keep check of a lot of stuff to make sure nothing is left unexplained at the end, but we also know that some unexplained stuff in a story make for good fan theory too