Heat oven to 350°F. In a large bowl, mix together cake mix, water, eggs, melted butter. Mix until smooth. Split batter into two bowls, tint one half purple and the other green. Spread onto a parchment-lined baking sheet or 9x13” pan, bake for 19-21 minutes, or until center of cake springs back when touched lightly. Remove from oven and cool completely.
In a stand mixer fitted with a whisk attachment, beat together softened butter, powdered sugar, vanilla and just enough milk to make a soft, fluffy frosting. Tint half purple and the other half green (or whatever colors you choose). Transfer into an icing bag, snip the tip toward the bottom to create a thin piping.
Tint remaining icing green or purple (to match the cake color). Transfer into an icing bag, snip the tip near the center to create a thick piping.
Crumble cooled cake. Mix a 2 Tbsp of frosting (the same color of frosting as cake) into the cake, use a fork to mix well. Open push pop containers, pull plunger to lowest position, set upright by pressing plunger sticks into the lids. Pipe a small layer of frosting in the bottom of each push pop. Press a thin layer of cake crumbs atop frosting, then pipe another thin layer of frosting, cake, frosting, cake, then a final bit of frosting, which peeks out over the top of the push pop container.
For the Monsters:
Top cake pops with a pile of orange frosting. Sprinkle with orange sprinkles.
Affix adhesive eyes to the front of the container. With a permanent marker, draw silly smiles and faces on the outside of the push pop container with a permanent marker.
For the Witches/Wizards:
Press a chocolate cookie atop push pop. Pipe a small amount of frosting in the center of the cookie, and press a chocolate kiss into the icing. Sprinkle with rainbow confetti sprinkles, if desired.
Affix adhesive eyes to the front of the container. With a permanent marker, draw on smiles and crooked witchy noses.