I'm writing a young adult fantasy with two main characters. Right now, I'm planning on writing it in 3rd person limited from the point of view of only one of the main characters. (Depending on how it goes, I might also add in the other main character's POV, but that's beside the point.)
All of the conflict that arises in the novel stems from a single villain, who has been masquerading as an ally of the main characters. I plan to keep the readers completely in the dark about the villain's true nature until the time is right and he's outed to the public -- I'm hoping it'll come across as shocking, at the very least.
My problem is this. I ran my plot idea to a friend of mine, and she said that my novel would be really confusing and frustrating to read if I only kept to a single character's POV. This is because many of the villain's actions affect the main characters in ways that seem to be unexplainable. For example, one of my main characters is someone who would never, ever try to kill someone. The villain manages (through the use of magic) to make that character kill someone. The main character does not realize that they were being swayed by magic.
With my current plan, readers will not know why the main character killed someone. I'm expecting them to be in the same position as the main character -- very confused. After all, they just did something totally out of character that even they can't explain. So readers can only suspect the reason behind it (until the villain is outed later in the novel and everything is explained). I will definitely give clues leading up to the villain's discovery, but nothing concrete.
My friend suggests that I switch to my villain's POV from time to time. For example, I could show him setting up the magic that would be used to get my main character to kill the person. However, I'm hesitant to do this because it would mean that my readers would definitely know the villain's true intentions. I wanted to keep his villain status as a surprise until later on. The confusion that emerged as part of the villain's plans was meant to be part of the story, something that would be explained when the time is right, but now I fear that my story will seem too confusing if I only stick with my main character's POV.
So, here are my questions. When would it be appropriate to switch the POV from my protagonist to my antagonist? Do you think, in this situation, doing so is a good move? Should transparency of plot be prioritized over shock factor/a surprising plot twist?