Preheat oven to 350 with rack on the lowest level.
In a stand mixer or large bowl add butter and peanut butter. Beat on low speed until blended together.
Add brown and white sugar. Turn mixer or beaters on high speed and beat for 3 minutes or until texture is fluffier and lighter than before.
Add eggs and vanilla to the bowl, mix only until combined.
Add baking soda and oats, mix well only until combined, do not overmix.
Add in chocolate chips and m&m’s and stir gently until everything is fully combined.
It's best to make bigger cookies for the right texture - so I would recommend using a 4 Tablespoon/1/4 cup size cookie scoop to form your cookies.
Place cookies on parchment lined baking sheet. Hand roll the cookies into round balls for best results.
Bake on the lowest oven rack 11-12 minutes, or until the bottoms of the cookies are browned on the edges.
Immediately after removing from oven, place a few extra m&m pieces and two candy eyeballs on top of cookies, and slightly press down.
Let cookies cool for 10 minutes before eating.
Keep any you aren’t eating right away to an airtight container at room temperature.