The actor who plays Jim's father is not the same man in the picture with the letter that Jim received about his father.
When one of the gang members pours beer on the Dragon Sound members' heads, John obviously leans in so the guy can reach him.
During Dragon Sound's performances, nothing is plugged into Tom or Mark's guitars.
During the creek fight, a ninja with his sword held high sneaks up behind John and obviously pauses, waiting for John to kick him.
Obvious lip syncing by Jane during her performance with Dragon Sound; she repeatedly moves away from the microphone with no effect on the volume or quality of her voice.
In the Dragon Sound performances, Mark's finger movements do not match the sound or tempo of the songs at all.
The song "Friends" has an obvious synthesizer bass line. Despite this, John plays the electric bass guitar, and Jim makes no attempt to play a bass line with his left hand on the synthesizer.
Stand with light reflector visible in the final scene in the hospital.
After John takes the sword and starts to fight the ninjas in the creek, a crew member in a white T-shirt is visible on a hilltop in the background. The camera angle changes and another crewman in an orange shirt can be seen.
At the end of the first confrontation between Dragon Sound and Jeff's gang, the film stock's perforations and grain are visible.
The main characters somehow finding where Tom's kidnapped.