Preheat oven to 325°F. Spray a 9-inch springform pan with baking spray or brush with melted butter. Optionally line the bottom with parchment paper.

Make the graham cracker crust. Mix graham cracker crumbs, 1/4 cup sugar, and melted butter until the mixture resembles wet sand. Reserve 1/8 cup crumbs for topping.

Press crust into pan. Firmly press the crumb mixture into the bottom of the prepared pan using the bottom of a measuring cup or glass to pack it evenly.

Bake the crust. Bake for 8-10 minutes until lightly golden. Cool completely before adding filling.

Beat cream cheese mixture. In a large bowl, beat cream cheese, 3/4 cup sugar, and vanilla on medium-high speed for 2-3 minutes until smooth and creamy. Scrape down sides frequently.

Add eggs. Switch mixer to lowest speed. Add eggs one at a time, mixing just until each is blended. Do not overmix.

Fold in marshmallows and chocolate. Gently fold in 1 cup mini marshmallows and 4 oz chopped dark chocolate using a spatula.

Assemble cheesecake. Pour filling over cooled crust. Top with remaining 1 cup mini marshmallows, 2 oz chopped chocolate, and reserved 1/8 cup graham cracker crumbs.

Prepare water bath. Wrap springform pan in 5-6 layers of heavy-duty aluminum foil. Place in a roasting pan and fill roasting pan with boiling water until it reaches halfway up the sides of the springform pan.

Bake. Bake for 55-60 minutes at 325°F. Center should still have a slight wobble.

Cool in oven. Turn off oven but keep door closed. Let cheesecake cool in water bath for 45 minutes. Do not open oven door.

Cool completely. Remove from oven and water bath. Cool at room temperature for 2-3 hours until completely cooled.

Chill overnight. Cover loosely and refrigerate for at least 4 hours or preferably overnight before serving.

Serve. Release from springform pan, slice with a hot knife, and drizzle with chocolate syrup if desired.