Prepare the cake mixes according to the package instructions, then set aside to cool completely.
Prepare the pudding according to the package instructions, then refrigerate to chill.
Add the oreos to a food processor and pulse until crumbled. Transfer 1/4 cup of cookie crumbs to a small mixing bowl, and set aside the rest. Add 1 drop of green food coloring to the 1.4 cup of cookie crumbs and stir until evenly combined.
Crumble both cooled cakes into the clean kitty litter tray. Add half of the plain cookie crumbs. Add half the chilled pudding, and stir until evenly combined. If the cake isn't moist enough, stir in more pudding- otherwise, save the rest of the pudding to enjoy later.
Add several tootsie rolls to a microwave safe plate, and heat just until soft/pliable. Gently stretch them and then lay them out haphazardly over the cake. I recommend doing at least 6 of these shapes.
Spread the remaining plain crumbled oreos evenly out over top.
Sprinkle the green cookie crumbs evenly out over top. You can use some of them, or all of them.
Heat 3-4 more tootsie rolls in the microwave, shape them, and nestle 3 of them on top of the cookie crumbs. Drape the remaining one down one corner of the kitty litter tray.
Serve with clean pooper scooper.