Preheat oven to 350°F and set aside a 9×13-inch baking dish.
In a large bowl, mix together graham cracker crumbs, sugar, and butter. Set aside 2 tablespoons of mixture, and press the rest into the baking dish.
Bake for 8-10 minutes. Remove from oven and set aside to cool.
For the filling, combine rhubarb and water in a large saucepan. Cook over medium-high heat until softened, 3-4 minutes. Stir in sugar, cornstarch, and jello until thickened and clear.
Pour over cooked crust and top evenly with mini-marshmallows. Chill in refrigerator until set, about 2 hours.
In a large bowl, mix together vanilla pudding mix and milk, then fold in frozen whipped topping.
Spread pudding mixture over marshmallow layer and place in refrigerator until set.
Sprinkle with reserved graham cracker crumbs, then slice, serve, and enjoy!