Buttercream, dyed a variety of different shades of green (recipe at www.pankobunny.com)
Make the pudding: Place the sugar, cocoa powder and corn starch in a pot and mix to combine. Gradually add the milk, stirring to combine. Set to low heat and bring to a boil. Boil for 2 minutes, stirring constantly, until thickened. Remove from the heat, pour into a bowl, add the vanilla extract and stir to combine. Cover the surface with a sheet of plastic wrap and place in the fridge until chilled.
Make the buttercream succulents: Spread some buttercream onto the surface of a flower nail, a tool that you use when piping buttercream roses etc. Place a square of parchment paper on top. Use a variety of piping tips to pipe the succulents of your choice onto the square of buttercream. This recipe used #67, #102, #102, #104, #18 and small, round tips for the cactus details. Slide the square of parchment paper onto a flat tray and transfer to the freezer until the succulents are very firm.
Spoon the chocolate pudding into glasses and top with some crushed oreos. Gently arrange the succulents inside the glass, then fill in the spaces with rock candy. Enjoy!