1. Line cookies in a single layer on a baking sheet with sides; set aside. In a medium mixing bowl, sprinkle gelatin over 1/3 cup cold water to soften.
2. In a small saucepan over medium-high heat, dissolve granulated sugar in 1/4 cup water, stirring. Remove spoon, brush inside edges of pan with water to remove sugar crystals and boil until the temperature reaches the soft-ball stage (238 degrees F) on a candy thermometer. Add mixture to gelatin and, using an electric mixer, whisk on medium speed for 3 min. Increase speed to high and whisk until soft peaks form, 8 to 10 min.
3. Transfer marshmallow to a piping bag fitted with a 1/2-inch-diameter plain tip, or coupler, and immediately pipe pointed mounds onto cookies (pipe just 5 ghosts at a time so marshmallow doesn't set before you decorate). Working quickly, add candy eyes and coat generously with crystal sugar. Allow ghosts to set about 1 hr before serving; store in a covered container for up to 2 days. Makes 22 cookies.