In medium bowl, stir cake mix (from cupcake mix box), oil and eggs just until dry ingredients are moistened (batter will be thick). Carefully spread evenly over crust. Squeeze marshmallow filling pouch (from cupcake mix box) as directed on box. Squeeze small amounts of filling randomly over batter (about 16 dollops). Marble by pulling knife through batter, being careful not to go deep enough to touch crust, then turn pan and repeat.