Stir together the sugar, cornstarch and salt in a medium saucepan. Add the milk and egg yolks and whisk together. Place over medium heat and cook, whisking continuously, as the mixture comes to a simmer and becomes thick, 5 to 6 minutes. Remove the pan from the heat and stir in the chocolate, butter and vanilla until smooth and fully incorporated. Divide between the six 300-milliliter glass tumblers and chill for about an hour.
Top the pudding cups with some of the crushed sandwich cookies. Add the gummies, partially burying them in the crushed cookies, as if they are emerging from the "dirt".
Write R.I.P. on the vanilla sandwich cookies with an edible marker, then place them in the glasses so that they stand upright and resemble tombstones.