Set a large saucepan over medium-low heat, about 3 on a 10-dial, and melt the salted butter for 2 minutes. Add the mini marshmallows and stir with slow circles for 4 to 5 minutes, scraping the bottom every 30 seconds, until they collapse into a smooth white mixture. Pull the pan from the heat at about 170°F and stir in the vanilla extract for 15 seconds. Don't let the mixture bubble hard because the sugar can tighten. You'll see the marshmallows lose their individual shapes and turn glossy, while the buttery vanilla smell becomes stronger near minute 4. The mixture should fall from the spoon in thick ribbons without visible marshmallow lumps. Keep it gentle. If it starts popping or turning tan, the heat is too high and the bars can set hard. (My first batch boiled, and the finished squares were noticeably tougher.) Low heat protects the marshmallow's soft structure.

Immediately add the Kellogg's Rice Krispies cereal in two additions while the marshmallow mixture is still about 150°F to 160°F. Fold for 60 to 90 seconds with a rubber spatula, lifting from the bottom and turning the cereal over while keeping the spatula close to the pan. Scrape the corners once halfway through. Stop as soon as every cluster looks lightly coated. Work longer and the cereal starts crushing into dense crumbs. Next, the cereal should stay visibly puffed and irregular while thin white marshmallow strands stretch between some clusters. You'll hear a soft crackle as you fold, and the mixture will feel sticky but not soupy. Halloween Party Food Rice Krispies need this brief mixing window because overworking compresses the cereal and makes each bite heavy. Keep it rough. Gentle folding preserves the cereal's airy crunch.

Transfer the warm cereal mixture into a parchment-lined 9 by 13-inch pan within 2 minutes of mixing, while it is still around 125°F to 135°F and flexible. Lay another sheet of parchment over the top and press with flat palms in short gentle passes for 30 to 45 seconds. Push the mixture into the corners without compacting it hard. Then leave it at 68°F to 72°F for 30 minutes. The slab should settle into an uneven level layer about 3/4 inch thick, with visible puffed cereal and a few natural ridges across the top. It should stop feeling tacky after about 25 minutes and lift slightly from the parchment at the edges. Press too firmly and the bars become tight instead of chewy. Don't chill it yet. Room-temperature cooling lets the marshmallow set without turning brittle.

Cut the cooled slab into 12 uneven rectangles with one firm downward motion per cut, then separate the pieces by about 1/2 inch. Melt the orange vanilla candy melts and green vanilla candy melts separately at 50 percent microwave power in 30-second bursts for 2 to 3 minutes total, stirring after each burst. Stop when each coating reaches 105°F to 110°F. Drizzle thin lines across the bars and press on exactly 24 candy eyeballs. Finally, scatter the black sanding sugar while the coating is still wet and let the decorated bars stand for 15 minutes at 68°F to 72°F. The drizzle should look glossy at first and then turn matte enough that a fingertip won't leave a mark. Halloween Party Food Rice Krispies look best with uneven drips and slightly crooked eyes. Overheat the coating and it can thicken or seize. Let them set. Controlled heat keeps the candy coating fluid and smooth.