Spongebob enters Sandy's dome without his water-filled helmet twice, and does not succumb to the effects of the air inside. The real reason why he isn't wearing one is that the production couldn't afford to animate it in stop-motion.
In the Christmas parade scene, right after Pearl Krabs gets turned into a jerk, she is seen just seconds later in the background, looking perfectly normal.
The song displayed as the antidote is not the same rhythm or notes that SpongeBob sings later to cure everyone.
At 17 minutes, Sandy shows SpongeBob the music antidote. The musical staff shows 6 lines and 5 spaces. A real musical staff has 5 lines and 4 spaces. Additionally, the measures do not all have 4 beats as the time signature indicates.
Patchy the Pirate's hook hand changes sides between scenes. He's an obviously fake pirate played for laughs. He switches his eye patch from eye to eye as well. He only has one to look like a pirate.