Bake cake according to package directions making one 9x13 size or 2 rounds. Let cool completely before using.

Whisk together milk and pudding and refrigerate until firm, about 5 minutes. Fold together with whipped topping to make a mousse. Set aside.

Place 12 Oreo cookies into a resealable bag and seal shut. Use a rolling pin to coarsely crush cookies. Place into a bowl and set aside. Repeat, so you have 2 bowls of 12 crushed cookies.

Place 6 Golden Oreo cookies into a resealable bag and add 10-12 (or more) drops of green food coloring. Seal shut and knead until green, or the desired shade for moss. Set aside.

Make mushrooms by melting chocolate chips in a resealable bag. Microwave for 60 seconds on 50% power and knead until smooth, returning to the microwave in 30-second increments at 50% power until melted and smooth.

Cut a few chocolate creme filled wafers with a knife. Place fudge cookies face down on a flat surface. Add a dollop of melted chocolate and gently press the creme filled wafers into the chocolate to create a stem. You may need to hold the wafer for a minute or two until the chocolate begins to harden. Repeat for the desired number of mushrooms and refrigerate until firm, about 10 minutes.

Remove mushrooms from the fridge and frost with red frosting and sprinkle with bits of white candy pieces. Place into a bowl filled with sugar for icing to harden a bit.

To assemble the terrarium: Pour rocks into the bottom of the glass jar.

Cut cake in half and break apart with your fingers and sprinkle on top of the rocks. Gently press into an even layer.

Top with the 12 crushed Oreos followed by the mousse. Top with remaining 12 crushed Oreos and half of cake, crumbling as you add the layer. If desired, add a few taller "cubes" of cake, to make some dimension within your terrarium.

Finely crush 6 Oreo cookies and sprinkle on top to create dirt.

Sprinkle green moss in any pattern you'd like on top of the cookies.

Add mushrooms, the easiest way to do this is to put them between your fingers as shown and press them into the cake. The frosting, usually thick, doesn't completely harden, and this is the easiest way to press them into the cake without damaging them.

Tuck in fresh herbs to create plants. Cover and refrigerate until ready to serve.