Spread the popcorn in a single layer over the parchment-lined baking sheet, removing any unpopped kernels.
Melt the orange candy melts with half the coconut oil in 30-second microwave bursts, stirring until smooth. Repeat with the purple candy melts and remaining coconut oil in a separate bowl.
Drizzle the melted orange candy melt over the popcorn in thin ribbons, then drizzle the purple candy melt over the top.
Immediately scatter the Halloween sprinkles and black sanding sugar over the still-wet candy coating.
Use two large spoons or your hands (lightly oiled) to toss the popcorn gently so the coating begins to coat individual pieces and clusters form.
Leave the tray flat at room temperature for 20 to 25 minutes until the candy coating is fully set.
Break into clusters and transfer to a large bowl or individual paper cones for serving.