Mix graham crackers and butter until well combined. Press into the bottom of an 8x8-inch pan, set aside.
Mix together ice cream and whipped topping in a stand mixer on low speed until combined. With mixer running, slowly pour in the vanilla and butterscotch pudding mixes; mix well, then add milk. Add 7 of the peanut butter cups, one at a time (they will break up as you mix them). Pour mixture into prepared pan, and top with remaining 9 peanut butter cups (one piece per slice).
Wrap well with plastic, and freeze 6 hours to overnight. To serve, cut into slices, and drizzle with chocolate syrup.