Place the Oreo cookies into a food processor in batches and process until they form fine crumbs. Transfer all the processed crumbs into a large bowl and set aside for assembly.

In a large bowl, whisk together the whole milk and instant chocolate pudding mix for about 2 minutes, until the mixture begins to thicken. Gently fold in the thawed whipped topping until there are no visible streaks, forming a creamy pudding mixture.

Drizzle 1/2 cup of the chocolate syrup into the pudding mixture. Gently swirl it a few times, so the syrup appears streaky through the pudding. Place the pudding mixture in the fridge until you are ready to assemble.

Arrange 18 serving cups (about 9 ounces each). Add 2 tablespoons of the Oreo crumbs (from Step 1) to the bottom of each cup. Spoon just under 1/4 cup of the pudding mixture (from Step 3) over the crumbs. Repeat with another layer: 2 more tablespoons of Oreo crumbs, then the remaining pudding. Finally, top each cup with 1 tablespoon of Oreo crumbs. I like to gently tap the cups between layers to even them out.

Stir the remaining 1/2 cup of chocolate syrup into the leftover Oreo cookie crumbs in a small bowl. Mix until the crumbs become clumpy and have a moist, uneven appearance. Set these aside for decoration.

Use black decorating icing to personalize Milano cookies with 'RIP' or spooky sayings. Gently press them into the tops of the cups to resemble gravestones. Add ghost-shaped marshmallow treats and mini pumpkin-shaped candies for extra Halloween fun, pressing gently so they stand upright. If desired, only decorate half the cups for variety. Sprinkle on assorted Halloween-themed sprinkles. Top each cup with some of the clumpy 'fresh dirt' cookie crumbs (from Step 5) to replicate freshly dug earth. I like to get creative with the designs—kids love decorating their own ghoulish cups!

Chill the decorated graveyard cups in the refrigerator until ready to serve, or enjoy them immediately for a spooky treat!