Question: Is Griffin always naked? Because his clothes (glasses) are visible but he is not.
Question: What is the last song from the end credits - the orchestral song during the concept artwork, not the "Problem (The Monster Remix)" song?
Answer: The last song I believe you're referring to was composed by Mark Mothersbaugh. However, there are no official names for the scores he composed. It would just be something like "End Credit Suite."
Answer: I a monster.
Question: During the party near the ending, why did the guests panic when they saw Jonathan's true identity?
Answer: Throughout the movie, Dracula has been drilling into his guests the history of humans' mistreatment of monsters, hence the building of the hotel, which was to be a monster's refuge from the human world. Most of the monsters likely had never interacted with humans, so that coupled with the stories from the past caused the monsters to freak when they saw Jonathan's true identity as a human.
But they had been hanging out in the hotel for long and johnny wasn't a bad person so the shock is unjustified.
Answer: Part of the shock would be him lying all this time, or the possibility of him being a fake Johnny.
Question: What did Dracula meant when he said he can't kill Jonathan?
Answer: Just what he said: it would set monsters back hundreds of years. Monsters are harmless, sociable creatures in this world yet humanity fears them. To kill a human would justify humanity's fears and set whatever progress monsters may have made toward being accepted in the world back hundreds of years.
Question: I don't quite understand, when all the other monsters find out Jonathon is actually a human, why does he suddenly decide he hates monsters? Wasn't he impressed with monsters even when he initially thought the ones at the hotel were people dressed in costumes?
Answer: There's a scene where he's wearing swim trunks which are visible, but he gets embarrassed when they're pulled down and he runs away. Obviously just meant to be a gag, but if the thought of people "seeing" him naked embarrassed him, one would think he must normally be dressed in clothes that can't be seen.
Bishop73