She wouldn't fully reveal herself to Jon until it's down to just him and his changes have started.
She could conjure up items that start the changes and plant them in places she know her targets will find them.
After doing a couple of changes to show Jon that she's serious, she could offer him the opportunity to stop the changes by completing a challenge she lays out but anyone who's completed their change is not eligible for this challenge.
At some point during the changes, they could end up at the stadium they're supposed to be at.
Just a few of the ideas I have at the moment to at least get us going.
