In a medium bowl, beat together cream cheese and butter until smooth. Sift in cocoa powder, then add brown sugar, vanilla extract, salt and milk. Beat on low speed until the cocoa powder is incorporated, then increase speed to high, until very well combined. Sift in powdered sugar, ½ cup at a time, beating slowly after each addition to incorporate. Increase speed to high and beat until smooth and light, about 3 minutes. Transfer dip to a serving dish and smooth top with a spatula.
Spread crushed chocolate cookies over the top of dip to form “dirt.” With decorating icing, write “RIP” on vanilla wafer cookies, then stand upright in dip to form “tombstones.” Scatter candy corn and candy pumpkins over top to decorate. Serve with graham crackers, sliced apples and/or pretzels as desired.