Preheat the oven to 350℉. Line a cupcake pan with cupcake liners.
In a large bowl, mix together the cake mix ingredients as called for on the box. Stir in the dry pudding mix until just combined. Do not over mix.
Spoon the cupcake batter into the lined cupcake tins until 2/3 of the way filled. Bake as directed on the box.
Cool for 10 minutes in the cupcake pan before transferring them to a wire rack to cool fully.
Make the frosting
Beat the butter and cream cheese until smooth.
With the mixer on low, slowly add the powdered sugar. Add the vanilla and mix until smooth and combined.
Frost the fully cooled cupcakes using a pastry bag and large tip or with a butter knife.
Make the Edible Blood
In a medium bowl, whisk to combine the corn syrup, and cornstarch, 1 Tablespoon of water.
Mix in the red food coloring.
Add a little bit of additional water to thin, if needed.
Decorate
If using, place a knife decoration into the center of each cupcake.
Drizzle the blood over the top of the cupcakes or dip a basting brush into the blood and shake the brush towards the cupcakes for a blood splattered effect (this can get messy).
Notes
Store in an airtight container in the refrigerator for up to 2 days.