Place popped popcorn in a large mixing bowl. Line a baking sheet with parchment paper.
In a microwave-safe bowl, melt white chocolate and red candy melts together in 30-second intervals, stirring until smooth.
Stir in cocoa powder, powdered sugar, and vanilla until combined (this gives the 'red velvet' flavor).
Pour the chocolate mixture over popcorn and toss until evenly coated.
Spread popcorn onto the prepared baking sheet in an even layer.
Drizzle red decorating gel or melted red candy melts across the top to create a bloody effect.
Allow to set at room temperature (or refrigerate briefly) until chocolate hardens.
Break into clusters and serve in bowls, paper cones, or spooky containers.