In the mirror dimension in Doctor Strange, one cannot affect the real world.
Doctor Strange: The Mirror Dimension. You can't affect the real world in here. Who's laughing now, a$%^ole?
Kaecilius: I am.
MORDO: Their connection to the Dark Dimension makes them more powerful in the Mirror Dimension. They can't affect the real world, but they can still kill us.
If they can't affect the real world, they cannot kill a person in the real dimension either, because whatever happens in the mirror dimension did not happen really.
Am I missing something here?