First, the Marshmallows will sort of pop into a million pieces. I think this because it seems quite similar to eggs in my opinion. Then, those little pieces will burn to a crisp and then melt into liquid.
See the experiment in action:
The Marshmallows went dry,chewy and crispy. They went chewy because the marshmallows got dry because they gradually steamed up. I think my prediction was about 50% correct.