Add the canola oil and kernels to a large pot over medium-high heat. Once the first kernel pops, cover the pot and pull it off the heat for about 30 seconds so the rest of the kernels heat evenly. This little pause is what keeps burnt kernels out of your batch.
Put the pot back on the burner and shake it back and forth firmly while it's still on the heat. Once the popping slows down to a few seconds between pops, take the pot off the stove completely. Pour all the popped popcorn into your largest mixing bowl.
Melt your white chocolate wafers or candy melts using a double boiler, or set a heatproof bowl over a pot of gently simmering water without letting the water touch the bowl. If you'd rather skip the stovetop step, melt it in the microwave in 20-second bursts, stirring between each one.
Pour the melted white chocolate directly over the popcorn in the bowl. Add the crushed Halloween Oreo cookies, candy corn, and sprinkles right on top. Toss everything together gently with a spatula until the popcorn is evenly coated and colorful.
Spread the popcorn out on a baking sheet lined with parchment paper for a few minutes so the chocolate firms up. Once it's set, break up any big clumps and pile it into a serving bowl or individual halloween popcorn bags for guests to grab.