Prepare macaroni and cheese according to directions on box. When it is done, stir in the cream of chicken soup & can of drained tuna. Slightly crush the Rice Krispies. In a frying pan on low heat, saute Rice Krispies in butter for 3-5 minutes. Pour macaroni and cheese mixture into casserole and spread evenly. Sprinkle on shredded cheese & then top with Rice Krispies. Bake on 400 degrees until cereal topping turns golden brown, about 15 minutes.