Line a 9 × 13-inch baking dish with wax paper. Pour the cereal into a large mixing bowl.
Melt butter and kosher salt in a large pot over low heat. Stir in marshmallows until completely smooth.
Remove from heat, stir in vanilla, and quickly mix the marshmallow mixture with the cereal until fully coated.
Spread gently into the prepared pan without pressing firmly. Cool completely for 45–60 minutes, then cut into 12 rectangles.
Melt the white, black, and orange candy melts in separate microwave-safe bowls until smooth.
Dip or spread the candy melts over the treats. Add candy eyes while the coating is wet.
Let the treats stand for 30–45 minutes, until the candy coating is firm.