Line a baking sheet with parchment paper and set aside.

Melt the semisweet chocolate chips in a microwave-safe bowl in 30-second intervals, stirring between each, until smooth. Let cool slightly.

In a medium bowl, whisk together powdered sugar, cocoa powder, and powdered milk.

Add the melted chocolate and vanilla extract to the dry ingredients. Stir until a thick dough forms.

Gradually add hot water, 1 tablespoon at a time, until the mixture comes together and is moldable but not sticky.

Divide the dough into 8 equal portions. Flatten each portion and place 2–3 mini marshmallows in the center. Wrap the dough around the marshmallows and roll into a smooth ball.

Place cocoa bombs on the prepared baking sheet and refrigerate for 15 minutes to firm up.

While chilling, melt white chocolate and candy melts separately. Use a piping bag or fork to drizzle melted white chocolate over the cocoa bombs.

Add green candy melt details for Grinch faces and red for tiny hearts. Sprinkle with edible glitter if desired.

Let decorations set completely at room temperature or in the fridge for 10 minutes before serving or gifting.