Add 9 cups of Chex cereal to a very large mixing bowl. Line a large baking sheet (or a section of your counter) with parchment paper; this is where the coated mix will cool and set.
9 cups Chex cereal
If using red velvet cake mix, spread 1/2 cup of red velvet cake mix in an even layer on a baking sheet. Bake at 300°F (150°C) for 5–7 minutes, stirring once halfway through. Let it cool completely before using.
1/2 cup red velvet cake mix
In a medium bowl, whisk together the heat-treated red velvet cake mix (if using), cocoa powder, and powdered sugar until no cocoa streaks remain. If you are using powdered buttermilk (no-cake-mix option), whisk it in here as well.
1/2 cup red velvet cake mix, 1 tablespoon unsweetened cocoa powder, 1 1/2-2 cups powdered sugar, powdered buttermilk
In a microwave-safe bowl, combine the white chocolate chips, unsalted butter, and fine sea salt. Microwave on 50% power for 30 seconds, then stir. Continue microwaving in 20–30 second bursts at 50% power, stirring each time, until about 75–80% of the chips are melted. Remove from the microwave and stir until completely smooth.
1 1/2 cups white chocolate chips, 2 tablespoons unsalted butter, 1/4 teaspoon fine sea salt
Stir the vanilla extract into the melted white chocolate. If you are making the no-cake-mix version and using red gel food coloring, add it now a little at a time, stirring well, until the chocolate is a deep red shade.
1 teaspoon pure vanilla extract, red gel food coloring
Pour the warm white chocolate mixture over the bowl of Chex cereal. Using a wide spatula or clean, gloved hands, gently fold until all of the cereal pieces look evenly and lightly coated, being careful not to crush the cereal.
9 cups Chex cereal, 1 1/2 cups white chocolate chips, 2 tablespoons unsalted butter, 1 teaspoon pure vanilla extract, 1/4 teaspoon fine sea salt
Add about half of the red velvet powdered sugar mixture to a large 2-gallon zip-top bag (or divide between two 1-gallon bags). Spoon the white chocolate–coated cereal into the bag, then add the remaining powdered sugar mixture on top. Seal the bag well and shake until every piece is coated. If some pieces still look shiny, add a few more tablespoons of powdered sugar and shake again.
9 cups Chex cereal, 1/2 cup red velvet cake mix, 1 tablespoon unsweetened cocoa powder, 1 1/2-2 cups powdered sugar
Spread the coated cereal in a single layer on the prepared parchment-lined baking sheet. Let cool and set for 10–15 minutes, or until the coating is dry to the touch. Gently break apart any large clumps.
Once fully cool, transfer the muddy buddies to a serving bowl and stir in Valentine-colored M&M’s or chocolate candies, sprinkles, and mini marshmallows if using. Serve immediately or store in an airtight container.
1-1 1/2 cups Valentine-colored M&M’s or chocolate candies, Valentine or holiday sprinkles, mini marshmallows