Preheat oven to 350 degrees. Grease a muffin tin (Jumbo size muffin tins are easier to use, but regular muffin tins will work.)
Mix the sugar and cinnamon in a small bowl until combined. Set aside.
Melt the butter in a small bowl. Set aside.
Separate the crescent dough into 8 triangles.
Dip each marshmallow into the bowl of butter and then roll it in the cinnamon-sugar mixture to fully coat. Place each coated marshmallow on a crescent roll triangle. Roll the dough around the marshmallow. Pinch the sides and any holes in the dough. Be sure the edges are completely sealed to avoid the marshmallow from oozing out.
Dip the tops of the stuffed rolls in the butter and cinnamon-sugar. Place the rolls in the muffin tins, sugar side up.
Bake for 10-15 minutes or until the rolls just turn golden brown. Remove from the oven and allow to cool slightly.