In a large nonstick skillet, stir 1/2 cup sugar and 2 tbsp. water over medium until sugar dissolves. Add the pecans. Cook, stirring often, until the sugar coats the pecans (you'll see white clumps), 5 to 8 minutes. Transfer the candied pecans to a baking sheet and let cool.
Line a 10-inch springform pan with two long sheets of plastic wrap, leaving a 6-inch overhang on all sides. Spoon the softened butter pecan ice cream into the pan; spread out in an even layer. Top with half the crushed cookies; drizzle with 1/2 cup caramel sauce. Set 14 pecan halves aside for the garnish (pick the prettiest ones). Scatter half the remaining pecans over the caramel sauce. Freeze until the ice cream is firm, about 2 hours.
Let the chocolate ice cream soften. Remove the cake from the freezer and spoon the softened ice cream on top of the pecans; spread into an even layer. Top with the remaining cookies, drizzle with the remaining 1/2 cup caramel sauce, then scatter with the remaining pecans. Freeze until firm, about 2 hours.
Let the pumpkin ice cream soften. Remove the cake from the freezer and spoon the softened ice cream on top of the pecans; spread into an even layer. Wrap the plastic wrap over the cake. Freeze until firm, about 2 hours or overnight.
In a small saucepan, melt the coconut oil over medium. Add the chocolate and stir until just melted, 3 to 5 minutes. Let cool to room temperature.
Remove the sides of the cake pan. Peel back the plastic wrap, then invert the cake onto a platter. Remove the pan bottom and the plastic wrap. Pour the chocolate mixture over the cake, spreading the sauce over the top so some of the sauce drips down the sides. Before the sauce sets, place the cherries and reserved pecans around the top edge of the cake. Serve immediately or freeze uncovered until the chocolate coating is firm, then cover loosely with foil and keep frozen. Let stand at room temperature 15 minutes before slicing. For easy cutting, dip a knife in a glass of hot water and wipe dry between slices.
Learn How to Make Creamy Caramel Sauce—Quick!