Teen Wolf's Stiles Stilinski is struggling to wrest his sanity from the Nogitsune, but soon he will be battling the dark spirit for his life.

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For three and a half seasons, Stiles (Dylan O'Brien) served as Teen Wolf's comic relief a Scott's problem solver. Now, however, the sarcastic teen is tapping into viewers' emotional nerve centers as the Nogitsune takes over his actions. Meanwhile, the true Stiles is trapped inside, struggling to seize control.

"We still see Stiles in every episode," O'Brien explained to Entertainment Weekly. "We see his struggle with not understanding; he clearly has no control over it. He goes in and out of being aware of it. And you see the Nogitsune getting stronger. So it just gets really dark and crazy....It becomes insanity, basically."

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Viewers will get a further taste of that insanity next Monday when Stiles checks into a mental hospital in "Echo House." Once there, a new sneak peek shows that Stiles appears to be in control while he is awake but something malicious will take place when he closes his eyes (see video below).

O'Brien's dramatic arc is set to go down to the wire, and when it come to a conclusion in the season finale, either the monster or the boy will be six feet under.

"The whole season for him is a struggle with himself - himself being, obviously, the spirit. It will be one or the other, basically," O'Brien told Entertainment Weekly. "So the finale is crazy because either he dies or the Nogitsune dies and no one knows how to kill the Nogitsune, so it gets weird."

Catch up with the Stiles/Nogitsune drama when Teen Wolf airs Mondays at 10 p.m. ET on MTV.

Tags: Teen Wolf MTV television