Melt each batch of chocolate chips in separate bowls, either in the microwave or set over a pan of simmering water. If melting in the microwave, heat each batch on high in 30-second bursts. Leave to cool until thick.
Dip a third of the pretzels into the white chocolate, a third of the pretzels into the dark chocolate and the remaining pretzels into the milk chocolate, then lay them all out on a sheet of baking parchment.
Add edible eyes to each pretzel (three eyes looks extra spooky). Leave to set, then peel carefully off the paper. Will keep in an airtight container for up to a week.