Mitsuki: unsurprised and somewhat pleased. She made a promise to Mercer that she would haunt him always in such event.
Anna: immediately try to make friends with all the ghosts haunting Hogwarts (assuming Hogwarts to be her haunting grounds) and start advocating for Sir Nicholas to become a proper member of the Headless Hunt and make it a personal goal to get Moaning Myrtle to smile and laugh
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What would your character (any age and perhaps the first one that comes to mind when you read this!) do if they could be a Legilimens for 24 hours? Whose mind would they want to delve into?