Line 2 pans with parchment paper and set aside.
In large bowl with an electric mixer combine melted butter, peanut butter, brown sugar, and white sugar, and beat until well combined.
Add eggs one at a time, beating well between each addition.
Add vanilla, corn syrup, salt and baking soda and beat until combined.
Mix in flour and oats until well combined.
With wooden spoon or spatula, mix in chocolate chips, butterscotch chips, and m&ms. Warning: you will get an arm workout doing this!
Let dough rest for 30 minutes...
Preheat oven to 350 degrees F.
Drop dough by 1/4 cup balls onto baking pans...these might seem big but they aren't called monster cookies for nothing!
Flatten cookies slightly and top with a couple more M&M's if desired.
Bake 14-15 minutes, until they are light golden brown. They will seem underdone but you do not want to overbake them! They will set up as they cool.
Let them cool on baking sheet for 10 minutes, then transfer to cooling rack to cool completely.
Serve and enjoy!
Store leftovers in airtight container. These also freeze well!