In large saucepan over low heat, melt margarine. Add marshmallows; stir until melted and well blended. Remove from heat.
Stir in vanilla, add the chopped Nim-Nums. Add cereal, stirring until coated.
Using lightly buttered spatula, press into a 3 1/2 L or 13″ x 9″ buttered pan.
Cool. Cut into bars.
In a water bath, melt the white chocolate and add the food coloring.
Pour the white chocolate in a tall glass or in a bowl. Take out a cooking sheet with parchment paper. Set aside.
Dip half of a square in white chocolate and add quickly the eyes candies and the nim-nums. Hurry, the chocolate gets solid fast. Put it on the cooking sheet. Repeat the process with all of the other squares.