Esmeraude summoned her to the Maxi-5 cake shop, and she undertook the disguise of a human waitress to wait until the Dark Henge started filling up the area with Dark Power. Mamoru realized that the "waitress" was not what she seemed, however, and attacked, and she dropped her disguise in response.
In her transformed state, Marzipan could turn her hands into piping tubes and fire out icing which turned objects struck by it into giant pastries and sweets. When the Sailor Senshi were hit by that attack, they were trapped in giant pastries, and their bodies became fragile like sugar candies.
Marzipan's body was apparently made of something similar to sugar and was thus vulnerable against water. After realizing this, Sailor Mercury attacked her with Shine Aqua Illusion, which weakened the Droid. The now-freed Sailor Moon then destroyed Marzipan with Moon Princess Halation.