After narrowly escaping a bizarre accident, a troubled teenager is plagued by visions of a man in a large rabbit suit who manipulates him to commit a series of crimes.
Frank the bunny rabbit is actually a version of a human called Frank, who Donnie shoots in the eye and kills towards the end of the movie. You see his eye injury at various points in the movie.
Not on screen. But Gretchen mentions her mother was stabbed by her step father. At the end she says she cannot find her mother and believes her step-father has came back (he fled arrainment) however because Gretchen is manipulated dead it’s unclear whether the latter is true/will still happen in the prime universe.
Donnie stabs at franks eyes and it flashes every time he does. During the scene where his parents speak to the therapist and it cuts back to Donnie in the bathroom with a knife.
Also there are interspersed scenes of cloud imagery which is sudden like a flash.
Roberta Sparrow (Grandma Death) is implied to have memory issues, as all she does all day is go back/forth to the mailbox. Seemingly forgetting she’s done so within moments.
Technically speaking Donnie’s mother is likely about to die upon the closure of the tangent universe because the engine is ripped from her plane. However this is not the prime universe which is restored by the action of removing the engine so it falls through the wormhole.
Donnie is having audio-visual hallucinations of Frank throughout the movie. Reality itself is unstable as the majority of the film is a paradox that Donnie needs to resolve.
Not on screen but Gretchen mentions that her step-father stabbed her mother in the chest multiple times and they have moved/changed their names as a result.
This is debatable as the ending/themes can be interpreted various ways as to what Donnie knew/thought would happen.
But the plot of the movie is that a paradox is occurring, to fix the paradox Donnie needs to close the loop by causing the plane engine to fall into his bedroom… where he is sleeping because he is no longer awoke by the manipulated dead (Frank). He seems to do this willingly to reverse Gretchen’s death and to save the universe and seems content in the knowledge he will die… or he is blissfully unaware upon briefly waking up. To each their own.
Nobody is possessed. In the tangent universe anyone who dies is considered “manipulated dead” and their goal is to push Donnie to resolve the paradox. This is Frank. However technically speaking Gretchen is the manipulated dead too throughout the whole movie.
Donnie has unnamed mental illness, it’s suggested to be schnizophrenia but we know his hallucinations are legit and why they are occurring. But he was in therapy for a while before the events of the movie so he does have at least anxiety/depression/emotional issues.