Prep the pan: Line a rimmed baking sheet with parchment paper. Clear space in your fridge so the bark can chill flat.
Melt the dark chocolate: Place semisweet or dark chocolate in a microwave-safe bowl. Microwave in 20–30 second bursts, stirring between each, until smooth.
Stir in 1–2 teaspoons oil if the chocolate seems thick.
Spread the base: Pour the melted dark chocolate onto the parchment and spread into an even rectangle about 1/4 inch thick. Aim for roughly 9x12 inches, but it doesn’t need to be perfect.
Add pretzels: Press mini pretzels gently into the warm chocolate in an even layer. You want them to stick but not sink completely.
Melt white chocolate: In a clean bowl, melt the white chocolate the same way.
If it’s too thick to drizzle, stir in a tiny bit of oil.
Decorate: Drizzle the white chocolate over the pretzels in zigzags. Sprinkle M&M’s, candy corn, and Halloween sprinkles over the top. Add a light pinch of flaky sea salt for a flavor boost.
Chill: Transfer the pan to the fridge for 20–30 minutes, or until the chocolate is fully set and firm to the touch.
Break and serve: Lift the bark using the parchment and place it on a cutting board.
Break into large shards with your hands, or use a sharp knife to cut neat pieces.