Start by breaking the sandwich cookies into chunks and pulsing them in a food processor until they resemble coarse soil. I like to keep a portion slightly chunkier for texture and grind the rest into fine crumbs. If you don't have a food processor, a zip-top bag and a rolling pin do the job just as well.
Whisk the cold milk and instant pudding mix together in a bowl for about two minutes, until it starts to thicken. Let it sit for a few minutes so it fully sets before you move to the next step. This is the base that gives your dirt cups that creamy, moussey texture everyone loves.
Once the pudding has set, gently fold in the whipped topping using a rubber spatula. Work in slow, sweeping motions so you don't knock the air out of it. The goal is a light, fluffy mousse that still holds its shape when spooned into cups.
Spoon a layer of cookie crumbs into the bottom of each clear cup, followed by a layer of the pudding mousse. Repeat the layers until you reach the top, finishing with a generous coating of cookie crumbs so it looks like fresh dirt. Drizzle a little chocolate syrup between layers if you want a darker, fudgier swirl.
Top each cup with gummy worms, candy pumpkins, or cookie tombstones pressed halfway into the crumbs. Cover the cups and refrigerate for at least an hour so the layers set and the flavors meld together before serving.