Boil potatoes and garlic until tender. Drain and return the mixture to the pan, shaking over medium heat until residual water evaporates and the potatoes look dry. Reduce heat to low and add buttermilk, butter and salt. Stir until butter melts, and then mash the potatoes with a masher or ricer, working out all of the lumps. If desired, beat potatoes with the paddle attachment of a standing electric mixer briefly. Set aside to cool.
While the potatoes boil, combine all the meatloaf ingredients -- reserving 1/4 of the ketchup to top the cupcakes -- in a large bowl. Gently knead mixture with your hands until it is well blended. Do not over mix.
Divide the meatloaf mixture among 12 standard-sized muffin tins. Top each cupcake with about 1 teaspoon ketchup. Bake in an oven preheated to 350° F until an instant-read thermometer inserted in the center reads 160° F, about 25 minutes. Let stand for 10 minutes before removing from the pan.
When you can handle the mashed potatoes without burning your hands, scoop them into a piping bag (or zip lock bag with the corner snipped off) fitted with a large round piping tip. If serving immediately, pipe a ghost atop each cupcake, smoothing down the tops with a fingertip if needed. Add allspice berries for eyes. If needed, reheat in the broiler to rewarm the potatoes.
To prepare ahead of time, pipe ghosts on a baking sheet or in a deep container. Add eyes. Refrigerate ghosts and prepared cupcakes separately. Right before serving, transfer potato ghosts to the meatloaf cupcakes using a sturdy metal spatula, pressing down gently to help them adhere. Reheat at 300° for 25 to 40 minutes in the oven, or simply reheat in your microwave.
If desired, drop cupcakes in colorful liners before serving.