Dr. Lawrence Gordon's long-awaited return in Saw 3D may count as this. This is considering the last time we saw him (in part 1), Lawrence was crawling away from his bathroom-prison, shivering from the blood-loss incurred from cutting off his foot and promising he'd find help for the still-shackled guy being tested with him (this is after he believes his family may well have been shot and killed due to his inaction in the "test"). In Saw 3D, he is a willing accomplice to John "Jigsaw" Kramer. In the first scene we see Dr. Gordon in during the present-timeline, he is delivering a cheesily villanous sounding monologue to the protagonist of the film, his smirking henchman demeanor majorly contrasting with the distrought husband/father he had become throughout the first film. Whatever real change occurred apparently happened completely offscreen, and what's more, apparently happened in the span of about 2 months, as we see Dr. Gordon smiling whilst placing a key behind a trap-victim-to-be's eye during a flashback that slightly predated part 2. At no point in Saw 3D does he mention his family or the guy he left behind, and ends up only looking at the latter's corpse rather dully during the climax when he returns to the bathroom.
An even better example is Jigsaw himself. Jigsaw made a huge point that he never killed anyone, merely put them in position where they had to fight and occasionally compete to live. Then in Saw VI he suddenly was fine with using Hoffman's traps, which did kill people outright.
Purposely done in the case of Susan Orleans in Adaptation. Portrayed as simply a reporter who develops a bond with John Laroche, due to Charlie Kaufman's in-story Creator Breakdown she proceeds to become a psychotic drug-addict who regrets her entire life.
