Carefully open up each Oreo and scrape off the creme filling, putting it aside in a bowl.

In a stand mixer fitted with the paddle attachment or a large bowl using a handheld mixer, whip the butter and Oreo creme filling for about 2 minutes, or until it's creamy and smooth. Mix in the vanilla extract and a small pinch of salt. Slowly add in the powdered sugar. Add the heavy cream or milk. Beat on medium-high for about 3 minutes, stopping to scrape the sides of the bowl as needed. Beat on low speed for about 1 minute to help remove any air bubbles.

Get 1 small bowl per color of food coloring you will be using. (i.e. I used 4 colors and got 4 small bowls.) Divide the buttercream frosting evenly into the bowls. Then using food coloring, stir into each bowl until the desired color is reached.

Using a small ziploc bag or piping bags with a round tip, put the different colors of frosting into each bag. If using a small ziploc bag, cut a small piece off of the corner so you can pipe it.

Taking one Oreo at a time, pipe on the frosting, starting around the edges first and then filling in the middle. Carefully take the other half of the Oreo cookie and gently push it on the top. Place candy eyes as you'd like on the Oreo monster and use sprinkles if desired. Repeat until all the Oreos are turned into Monster Oreos.

These don't have to be chilled right away, but I like to chill it a little so when you bite down on it the frosting won't come out of the sides.

Enjoy a spooktacular treat!