Heat oven to 350°F (325°F for dark or nonstick pans).
Place paper baking cup in each of 12 regular-size muffin cups.
In large bowl, beat cake mix, water, oil and egg with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally.
Divide batter evenly among muffin cups.
Bake 17 to 22 minutes or until toothpick inserted in center comes out clean.
Cool in pan 10 minutes; remove from pan to cooling rack.
Cool completely, about 30 minutes.
In small bowl, mix frosting and marshmallow creme.
Spoon into small resealable food-storage plastic bag; seal bag.
Cut 3/8-inch tip off 1 corner of bag.
Pipe 3 small dollops of frosting mixture on top of each cupcake to look like melted marshmallows.
Sprinkle with cocoa.
Press pretzel half into side of each cupcake for cup handle.