Drain pineapple: Drain crushed pineapple using a fine mesh strainer, reserving 2 tablespoons of the juice. Discard any remaining juice.
Combine pineapple, juice, and pudding mix: Place pineapple, reserved juice, and pudding mix in a medium bowl; stir to combine.
Add whipped topping, marshmallows, and walnuts: Add whipped topping, marshmallows, and walnuts; stir gently until mixture is combined and light green in color. Cover and chill for at least 1 hour or up to 2 days.
Prepare to serve: Divide salad evenly among 4 glass cups. Top each evenly with marshmallows, walnuts, and a maraschino cherry.
