Goof (errors made by characters, possibly deliberate errors by the filmmakers): The spelling of character's names change throughout the series. For example, Ofdenson's name is spelled Offdenson and Dr. Rockzo's name is spelled Dr. Rockso.
Goof (continuity error): When Nathan is in his pastel shirt, his hair is cut. However, in the next scene, his hair is regular length again.
Goof (continuity error): While Nathan Gives his speech at Harvard, just after he throws the paper away, you see the accountant standing just a few feet from him. The camera quickly changes to a wide shot and the accountant has disappeared.
Goof (continuity error): In the scene where Dethklok goes to see Prayerbolt, the lead singers guitar changes. The last time it is shown from a distance, the head is a cross. (Note: The 2nd guitar that the lead singer uses was the "guitar made with wood from Christ Cross" that was designed by Skwisgar in "Skwisklok")
Goof (revealing mistake): There are two Zs visible on the Scrabble board despite there being only one in the game.
Goof (continuity error): The band has to renegotiate their contract with the record label. The band is absolutely stupid when it comes to this and acts like they can't understand all of the legal "mumbo-jumbo" involved with renegotiating their contract. However during the Season 1 episode "Bluesklok", the band understands negotiating a contract like it's the back of their hand. So much so that the devil wants nothing to do with them after they made a few amendments to the devil's original contract.
Goof (factual errors): The truck of jet fuel stolen by Dr. Rockzo is improperly marked with the placard for propionaldehyde, a chemical used in plastic production. The number for jet fuel would be 1863.