Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
In a large bowl, combine the Devil's Food cake mix, eggs, and canola oil until a soft dough forms. Add black food coloring if desired.
Scoop dough into 1.5-inch balls and place on prepared baking sheets about 2 inches apart. Bake for 10 to 12 minutes until edges are set.
Allow cookies to cool completely on wire racks.
For frosting, beat softened butter until light and fluffy, then gradually add powdered sugar, vanilla extract, salt, milk, and green food coloring until smooth.
Spread frosting over cooled cookies, decorate with sprinkles and candy eyeballs, and insert pretzel sticks as stirring wands.