In a small saucepan, combine the rice, water, and green food coloring. Let it sit for 30 minutes. Bring to a boil, then reduce heat, cover, and simmer until the rice is tender and water is absorbed, about 10–12 minutes. Remove from heat, drizzle with seasoned vinegar, and stir with a slicing motion using a wooden paddle or spoon to cool slightly. Cover with a damp cloth to keep moist.
Place half the rice on a sushi mat or clean dish towel lined with plastic wrap. With moistened fingers, press the rice into an 8-inch square. Top with one nori sheet. Set aside eight carrot matchsticks. Arrange half of the cucumber, avocado, and remaining carrot about 1-1/2 inches from the bottom edge of the nori. Roll up the rice over the filling, using the mat or towel to lift and compress. Remove the plastic wrap as you roll. Slice the roll into four pieces using a wet, sharp serrated knife. Repeat with the second nori sheet and the remaining rice, cucumber, avocado, and carrot.
Shred the remaining nori sheet to look like hair strands. With wet hands, press the strands onto the rice. Halve the reserved carrot matchsticks and press two into each roll to look like bolts.
Add black food coloring to the prepared wasabi, then pipe spooky facial expressions onto each sushi piece. Refrigerate until serving.