Heat a grill or grill pan to high heat. Place a metal baking sheet in the freezer to chill.
Put the waffle cones in a large resealable bag or food processor. Crush the cones until ground to the texture of coarse sand. Put the crushed cones in a large bowl, add 10 tablespoons of the melted butter and mix until well combined. Transfer the mixture to a 9-inch pie dish and press to form a crust. Place in the freezer to set, about 30 minutes.
Slice the unpeeled bananas in half lengthwise (keep the peels on). Brush the cut sides with the remaining 2 tablespoons melted butter. Sprinkle each with brown sugar, then grill until grill-marked, 3 to 5 minutes. Let cool to room temperature, then peel and slice into 1/2-inch-thick slices.
Beat the heavy cream with the confectioners' sugar and vanilla in a chilled large metal bowl until it holds medium-stiff peaks. Transfer to a piping bag fitted with a large star tip and refrigerate until ready to use.
Using a small ice cream scoop (about the size of a golf ball), scoop out 4 scoops of each flavor from the Neapolitan ice cream and place on the chilled baking sheet. Return to the freezer. Let the remaining ice cream soften up a little, 5 to 10 minutes at room temperature.
Using a microwave or a bowl of hot water, slightly warm 1/2 cup of fudge sauce until pourable. Remove the crust from the freezer and spread the fudge on the bottom of the crust, using a spoon or an offset spatula to evenly distribute. Arrange the banana slices in a single layer on top of the fudge layer, pressing gently to adhere the bananas to the fudge. Scoop out the softened ice cream (all 3 flavors) on top of the bananas and, using a large spoon or an offset spatula, spread to cover the bananas, being sure to make the top as smooth as possible.
Place the small scoops of ice cream around the outside of the pie, alternating flavors, to create a border. Pipe the center of the pie with stars of whipped cream in a concentric circle, with one large star in the middle. Place in the freezer until the ice cream firms up, at least 4 hours and up to overnight.
To serve: Arrange 6 of the cherries on top of the pie, one between every other ice cream scoop. Place the walnuts in between the remaining ice cream scoops. Warm the remaining fudge sauce and drizzle all over the ice cream in concentric circles. Sprinkle the sprinkles around the border of the pie. Place the last remaining cherry in the center. Let sit at room temperature for about 10 minutes before slicing.