Unwrap 6 ice cream sandwiches and arrange them in a single layer in a 9x13-inch baking dish.
Spread half of the whipped topping evenly over the sandwiches.
Drizzle half of the hot fudge sauce over the whipped topping.
Repeat with another layer of 6 sandwiches, the remaining whipped topping, and the rest of the fudge sauce.
Sprinkle mini M&M's or crushed Oreos on top.
Cover and freeze for at least 2 hours or until firm.
Slice and serve chilled.