Preheat your oven to 325°F (160°C). Grease the sides and bottom of the springform pan and line the bottom with parchment paper.
To make the crust, combine the graham cracker crumbs, melted butter, and sugar in a mixing bowl. Mix until the crumbs are evenly coated. Press the mixture firmly into the bottom of the prepared pan to form an even layer and set aside.
In a large mixing bowl, beat the softened cream cheese with an electric mixer until smooth. Gradually add the granulated sugar and continue to mix until well combined.
Add the vanilla extract and eggs, one at a time, mixing until fully incorporated after each addition. Make sure to scrape down the sides of the bowl as needed.
Mix in the sour cream and cocoa powder until smooth. Pour in the melted chocolate and mix until fully combined.
Gently fold in the assorted candy pieces, reserving a handful for topping later.
Pour the cheesecake filling over the crust in the springform pan, spreading it evenly. Tap the pan on the counter to remove any air bubbles.
Bake in the preheated oven for 60 minutes, or until the edges are set and the center is slightly jiggly. Turn off the oven and crack the door open, letting the cheesecake cool in the oven for 1 hour.
Remove the cheesecake from the oven and refrigerate for at least 4 hours, or overnight, to fully set.
Once the cheesecake is set, remove it from the springform pan. Top with whipped cream and sprinkle with reserved candy pieces as desired.