Whisk the chocolate pudding mix with cold milk for 2 minutes until thickened. Refrigerate for 5 minutes to firm slightly.
Use the white tube gel icing to write "RIP" or a short epitaph on the cream side of each Oreo half. Let the writing set for 5 minutes.
Spoon the chocolate pudding into each cup, filling about three-quarters full.
Scatter a generous layer of cookie crumbs over each pudding cup to look like fresh earth.
Press two Oreo tombstone halves into the crumbs at the back of each cup so they stand upright.
Tuck a gummy worm into the crumbs at the front of each cup so it appears to emerge from the dirt.
Refrigerate for at least 1 hour before serving, adding the tombstones and worms just before serving if you want them fresh-looking.