Despite being able to create perfect duplicates of the townspeople, Niman's copies of RyuKenDo and RyuGunOu have purple visors instead of blue and red respectively. However, no one notices this.
It is unclear why Kenji initially chose to put on his demon mask to fight as it would block much of his vision and, as shown with the police chiefs, get him attacked by his own people who mistook him for a real demon.
As God RyuKenDo chases Jamaindo, the wires used to make it fly are briefly visible.
As Dr. Worm glues the pieces of Rock Crimson together, he puts the tube of glue down next to him and it immediately falls over. However, in the following shot from a slightly different angle, the tube is stood upright.
The money that Kaori returns to Koichi is, as ZanRyuJin says, British currency, specifically a £10 note. £10 is worth approximately ¥1500.