For the crust: Preheat the oven to 350 degrees F. Spray a 9-inch nonstick springform pan with nonstick cooking spray and line with parchment, separately on the bottom and a collar around the sides.
Mix together the pretzels, butter, sugar and cookie crumbs in a large bowl. Press the mixture into the bottom of the prepared pan. Bake the crust for 8 minutes. Set aside while you make the cheesecake. Reduce the oven temperature to 325 degrees F.
For the cheesecake: Melt the chocolate in the microwave or using a double boiler until smooth. Set aside.
Beat the cream cheese and sugar in a stand mixer with a paddle attachment on medium speed until very smooth, about 1 minute, scraping the sides of the bowl as necessary. Turn the mixer to low, add the sour cream and cocoa powder and mix until combined, scraping the sides of the bowl as necessary. Add the melted chocolate and then the eggs one at a time, mixing on low speed after each addition just until mixed; do not overmix. Pour the filling over the crust and spread into an even layer.
Double-wrap the bottom of the springform pan with foil, sealing it tightly to prevent water from getting into the pan. Place the springform pan into a larger pan and pour very hot water into the pan until it is about 3/4 inch deep, being careful to make sure the water level doesn't come up higher than the foil.
Bake until the center is almost set, 60 to 70 minutes. The center will still jiggle, while the edges will be set. Crack the oven door and allow the cake to cool in the oven for 1 to 2 hours.
Remove the cake from the oven and refrigerate for at least 4 hours and preferably overnight.
For the chocolate topping: Add the dark chocolate and coconut oil to a double boiler and heat until melted. Let cool slightly, then pour over the cheesecake, spreading so that the sauce drips slightly over the side. The chocolate will harden quickly, so immediately decorate the top of the cake with any additional toppings such as Cookie Pretzel Bark. Cut into wedges and serve chilled.
Cookie Pretzel Bark:
Line a small baking sheet with parchment.
Place a large glass bowl over a pot of simmering water so that the bottom of the bowl is not touching the water and add the chocolate. Heat until melted.
Spread the chocolate into a thin layer on the parchment. Sprinkle the crushed pretzels and cookies on the melted chocolate and place in the freezer until completely hardened, 10 to 15 minutes. Break into pieces and use to decorate the top of the cheesecake.