Pour the popcorn into a large bowl, remove any unpopped kernels, and set it aside.
In a medium saucepan, combine mini marshmallows, butter, and peanut butter. Melt over medium heat, stirring constantly, until the mixture is smooth and creamy.
Pour the peanut butter marshmallow mixture over the popcorn and stir to fully coat the popcorn.
Mix in 1 cup of the Butterfinger bits, then transfer the popcorn onto a baking sheet lined with parchment paper or a silicone baking mat.
In a microwave safe bowl, combine the chocolate chips and vegetable oil. Microwave in 30 second intervals, stirring in between, until melted and smooth.
Transfer the melted chocolate into a ziploc bag, cut off one end, and drizzle the chocolate over the popcorn.
Sprinkle the remaining ½ cup Butterfinger bits over the top of the popcorn.
Let the chocolate set completely, then break into pieces!