To make the 6 ghosts, in a microwave-safe bowl, microwave the white chocolate or candy melts in 30-second intervals, stirring in between, until melted and smooth.

Place a large piece of parchment on counter. Using a spoon, dollop 6 (1 teaspoon) portions of melted chocolate onto parchment spacing apart. Using the back of a spoon or an offset spatula, smear each portion into a 4-inch ghost shape across the parchment. Let cool 10 minutes to set. Once ghosts are set, pipe on eyes and mouth with the decorating gel.

For the 6 spiderwebs, place 2 cupcakes on cutting board. Working in batches, place 4 marshmallow quarters on a microwave-safe plate. Microwave 30 seconds, until puffed and soft. Let cool 10 seconds. Working with 1 marshmallow quarter at a time, squeeze and pull marshmallow between fingers to make a web. Immediately wrap web around 1 cupcake, using cupcake liner to secure web. Repeat with another marshmallow quarter onto cupcake. Repeat process with next cupcake, wrapping with 2 marshmallow quarters. If marshmallows are too hard to pull, microwave 10 seconds.

Continue to melt marshmallows and wrap cupcakes in spiderwebs until all 6 are complete. Let stand 10 minutes, until set. Top cupcakes with spider rings, if desired. Carefully remove ghosts from parchment and stick in remaining 6 cupcakes.