Make frosting: Using an electric mixer, beat butter until fluffy, 3 minutes. Reduce speed to low and mix in 1 cup confectioners’ sugar. Increase to high; beat 1 minute. Repeat, adding vanilla and 1 cup sugar. Reduce speed again; mix in cream and remaining sugar. Once incorporated, beat on medium-high speed until creamy and white, 4 minutes. Transfer to a large piping bag fitted with a large round tip. Pipe onto cupcakes. Make spiders: On a large piece of waxed paper, using black Royal Icing, pipe small spider heads, bodies, and legs as well as spiderwebs. Let dry at least 1 hour. To remove, rub a finger under paper to loosen. Make spiderwebs: Melt purple candy melts and transfer to a piping bag. Snip off a corner and pipe webs. Let set, then place on cupcakes. Make spiders’ nests: Fill a large bowl with 3 inches cold water. Line a large baking sheet with a reusable baking mat. Place 4 glasses on either end of long sides of baking sheet. Grease handles of 2 long wooden spoons and balance on glasses over cookie sheet. Place sugar, water, and corn syrup in a heavy-bottomed medium saucepan. Melt sugar on medium, swirling pan. Increase heat and boil, swirling pan occasionally and brushing down sides with water until it reaches 300°F. Immediately place base of pot in cold water until temperature registers 275°F. Working in batches, drag a fork through sugar and wave quickly back and forth over spoon handles to create long strands. Carefully collect strands into a ball with hands and place on top of cupcake. Repeat with remaining sugar syrup.