Prepare the baking sheet. Butter a baking sheet and generously dust it with powdered sugar. Set aside.

Bloom the gelatin. Combine gelatin and ice water in a small bowl. Set aside.

Make the syrup. Combine sugar, salt, corn syrup, and water in a saucepan. Bring to a boil, reduce heat to medium, and cook until the mixture reaches 243–245°F.

Whip the marshmallow. Add the bloomed gelatin to the bowl of a stand mixer. Carefully pour in the hot syrup. Beat on medium-high for about 13 minutes. Add vanilla and beat another 1–2 minutes.

Pipe the ghosts. Immediately transfer the marshmallow to a piping bag fitted with a large open round tip, or cut the end from a disposable frosting bag. Pipe approximately 30 ghost shapes onto the prepared baking sheet.

Rest. Let the ghosts sit for about 20 minutes.

Make the faces. Mix cocoa powder and water until smooth. Use a toothpick or lollipop stick to dab two eyes and a mouth onto each ghost. Let dry completely.

Dust. Lightly dust the ghosts with powdered sugar.

Set. Let the marshmallows sit uncovered for 4–6 hours. Pat additional powdered sugar onto any remaining sticky areas before serving.