Ah, for something like Shikamaru's shadow skills from Naruto? Seems tough for me though...
I have an idea for an event system, but I'm not much into events. You need to make a common event, and make an event move when you press the direction keys. That event will be your shadow. Place that event just below your hero. Now make an actor in the database, named 'the shadow' (or w/e). Now, when you want to switch control to the shadow, use some events and a change hero event command.
This might/moght not work, events are not my forte, so I don't really know how things might work out. For the time being, this script is beyond my level.