In a large pot over low heat, combine 4 cups of fresh marshmallows with 2 tablespoons of butter. Stir continuously until melted and smooth, about 5 minutes.

Add 6 cups of Fruity Pebbles cereal to the melted marshmallow mixture. Gently fold and mix until evenly coated, about 2-3 minutes.

Lay a large piece of parchment paper on your countertop and grease your hands with butter. Transfer the mixture onto the parchment, spreading it evenly into a rectangular shape about ½ inch thick.

Spoon any desired fillings like Nutella, mini chocolate chips, or shredded coconut over the surface and spread them evenly.

Starting from one end of the parchment paper, gently lift the edge and begin rolling the mixture tightly away from you. Roll until you reach the opposite edge and place seam-side down.

Using a sharp knife, slice the sushi log into bite-sized pieces. Arrange the pieces on a platter for a vibrant presentation.