In a large sauce pan melt the butter on low heat. Add in the marshmallows and stir until melted.
For the Sushi Roll
Remove from the heat and stir in Rice Krispies cereal. Stir until well coated.
While still warm, take a cup of the Rice Krispies treats and press out onto a 6 x 4 inch piece of black fondant that has been rolled out on a large sheet of waxed paper. It helps to butter your hands when working with the Rice Krispies mixture.
Lay several piece of the gummy worms, Sweet Tart ropes and other candies crosswise on the Rice Krispies layer.
Begin rolling tightly until you have formed your "sushi" roll.
Trim ends and slice into 6 even pieces. Arrange on a platter.
For the Nigiri Pieces
Take large tablespoons of Rice Krispies and form into rectangular shapes or use a Nigiri mold.
Place one Swedish Fish or Candy Fruit Slice on each piece. Slice fondant or fruit leather into ½ inch strips and wrap around each Nigiri piece. Place on a platter.
Experiment with other candies to come up with your own creative "Sushi" pieces.