Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone baking mat. In a large bowl, mix the cake mix, melted butter, eggs, and vanilla extract until well combined. Add green gel food coloring, mixing until the dough reaches a vibrant Grinch-green color. Chill the dough in the refrigerator for 15-20 minutes.

Scoop about 1 tablespoon of chilled dough and roll into balls. Generously coat each ball in powdered sugar and place on the prepared baking sheet about 2 inches apart. Bake for 8-10 minutes until cookies are set with a crackled surface but remain soft and chewy. Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Melt chocolate chips with coconut oil in a microwave-safe bowl by heating in 20-second intervals, stirring until smooth. Using a piping bag or a ziplock bag with a corner cut off, pipe a small dot of melted chocolate in the center of each cookie and press a red heart-shaped candy onto it. Pipe two upward-curved lines on each side of the heart to form the smile and add small lines above the smile and between the eyes. Let the chocolate set for 10-15 minutes at room temperature or refrigerate for quicker setting.