MAKE THE CHOCOLATE DOUGH: In a medium bowl, mix the finely crushed chocolate biscuits, melted chocolate, and sweetened condensed milk until a soft, fudgy dough forms. Adjust texture if needed by adding a bit more condensed milk if too dry or more crumbs if too sticky. Chill the dough for 10 minutes to firm up.
SHAPE THE BITES: Scoop about 1½ tablespoons of dough. For plain bites, roll into smooth balls or dome shapes. For filled bites, flatten the dough in your palm, place a mini marshmallow in the center, wrap the dough around it, and roll gently to seal. Place each bite on a parchment-lined tray.
CHILL TO SET: Refrigerate the shaped bites for 20–30 minutes, or until firm enough for decorating.
DECORATE: Melt the white chocolate in one bowl. In separate bowls, melt the red candy melts, blue candy melts, and chocolate chips. Use a spoon, fork, or piping bag to drizzle each bite with colorful stripes. While the drizzle is still wet, add red sprinkles or edible glitter. Chill for 5 minutes to set the decorations.