Cover tops of cupcakes with buttercream. Cut 6 marshmallows in half, and squish to make them slightly smaller. Using a wet toothpick, make two holes in each squished marshmallow, and insert sprinkles to create eyes. Use one piece of gummy fish for the nose.
Place a dab of icing on the tops of the remaining 12 marshmallows. Place a squished marshmallow on top of each to create the head. Place a dab of icing on each head, and top with a chocolate candy for a hat.