To combine the frostings, lay out two pieces of plastic wrap. Add the frosting to the wrap, and then roll it up into a tube shape, twisting the ends to seal. Snip off one of the twisted ends from each tube.
Add a star tip to a large piping bag, then add both colors of frosting, with the open end of the rolls pointing down toward the tip. Add a swirl of buttercream to each cookie, then top with a gummy shark.