Cake frosting

The deck of the Chicago Overcoat, covered in cake frosting.

Cake Frosting first appears in Problem Sleuth, when Past-Future Pickle Inspector uses Cake Frosting to extinguish the flaming pie filling.

Harlequin with arms

The harlequin doll with arms attached by frosting

Cake frosting serves a bigger purpose in Homestuck. John uses it as an adhesive to attach fake arms to the harlequin doll that would prototyope his kernelsprite. Although one of these arms is knocked off before the prototyping, the cake frosting is the cause of the one arm that Nannasprite does have.