As I write this, I should be cutting out leaves and two large cardboard waves. Be jealous of my evening.
1 cake mix, flavor of choice
Try to get your icing smooth, but, don't worry about it being perfect! It's supposed to be a Halloween cake! Now, take two halves of Oreos with the frosting on them, and put two of them close together. I had a few extra candy eyes laying around, so I put those on, too!
I melted some chocolate, since I didn't have any small M&M type candy laying around the house. I used a toothpick to draw some pupils onto the Oreos. If you have some small candy, you can use either some melted chocolate or frosting to stick them on for the pupils; Reese's Pieces or Skittles would make for some fun, creepy colored eyes!