Preheat the oven to 350°F (175°C).
Combine the crushed pretzels, melted butter, and brown sugar until evenly moistened.
Press the mixture firmly into the bottom of a 9x13-inch baking dish.
Bake for 10 minutes, then allow the crust to cool completely.
Beat the softened cream cheese, sugar, and vanilla until smooth.
Fold in the whipped topping until light and fluffy.
Spread the cream cheese mixture evenly over the cooled crust, making sure it reaches all the edges.
Dissolve the mango gelatin in the boiling water and let it cool until slightly thickened.
Stir the diced mango into the cooled gelatin.
Carefully spoon the mango mixture over the cream cheese layer.
Sprinkle crushed pretzels over the top if desired.
Refrigerate for at least 4 hours, or until fully set.
Slice into squares and serve chilled.