Using a handheld or stand mixer with a paddle attachment, beat the softened butter on medium speed until creamy, about 2 minutes. Add 5 and 1/2 cups (660g) confectioners’ sugar, heavy cream, and vanilla extract. Beat on low for 30 seconds, then medium-high for 2 minutes. Taste and add a pinch of salt if too sweet. To reduce air bubbles, gently fold the frosting with a spatula for 1–2 minutes.

Adjust the thickness by adding up to 1/2 cup (60g) more confectioners’ sugar if too thin or 1 tablespoon increments of heavy cream if too thick, beating and tasting after each addition.

Divide frosting into 5 bowls if making all 4 designs. Tint with gel food coloring: green, purple (mix fuchsia + violet), black (less quantity), orange, and keep one bowl white for spiders. Add a tiny dot of black gel to tone down brightness if needed. Stir well and note colors darken slightly over time.

Fit a piping bag with a small open star tip (Wilton #21) and coupler. Fill with green frosting. Pipe a spiral from outside to center on each cupcake. Place a large candy eyeball gently in the center, pressing lightly to adhere.

Using the same star tip and coupler, fill a piping bag with purple frosting. Pipe stars covering the entire cupcake surface. Press small candy eyeballs into the frosting and optionally add sprinkles.

Fit piping bags with a large petal tip (Wilton #125) for orange frosting, a star tip (#21) for green frosting, and a small round tip (#4) for black frosting. Pipe vertical curved lines with orange frosting to create pumpkin ridges. Pipe a green stem at the top. Use black frosting to pipe eyes, nose, and mouth, customizing spooky or goofy expressions.

Spread white frosting evenly on the cupcake with a small offset spatula. Use a piping bag with a small round tip (#4) filled with black frosting to pipe three criss-cross straight lines forming 6 triangles, then connect these with curved lines to create a spider web. Press half a mini Oreo cookie on the web as the spider body, pipe two tiny black dots for eyes, stick mini candy eyeballs onto them, and pipe 8 spider legs extending from the Oreo piece.

Store cupcakes uncovered at room temperature for a few hours before serving. For longer storage, cover and refrigerate up to 5 days. Use a cupcake carrier for transport.