Character mistake: When Mandi brings out Golbat, Brock says, "Kingler is really weak to air attacks." But Kingler's a Water type, which has no weakness to Flying-type attacks.
Suggested correction: Brock is saying that Kingler is vulnerable to attacks from the air, not that it is weak to Flying-type moves.
Character mistake: When Team Rocket first sees Mandi doing his magic tricks, he produces a bunch of Pidgey. Meowth says "I like those Pidgeotto." He's dealt with Ash's Pidgeotto on numerous occasions, so there's no reason that he shouldn't be able to tell the difference. [This mistake only appears in the English version. In the Japanese version Meowth doesn't even mention Pidgey nor Pidgeotto at all.] (00:04:49)
Continuity mistake: When Brock mentions that Ash has to win on the rock, grass, water, and ice fields to compete at the Indigo Stadium, a staff member of the Pokémon League is not smiling, but in the next shot, she is. (00:03:07)
Continuity mistake: When Professor Oak and Delia are first seen watching Ash's first battle at the Indigo Plateau Conference, Delia has a person to the left of her, and her hands are in her lap, but in the next shot, she does not have a person to the left of her, and her hands are clasped together. Also, she and Professor Oak are smiling, but in the next shot, they are not. (00:11:46)
Continuity mistake: When the Officer Jennys say that the news reporters are Team Rocket, Meowth's disguise disappears. (00:12:31)
Continuity mistake: When Ash agrees to the fact that this is his first time at a Pokémon League, the front part of his hat does not go past the visor, but in the next shot, it does. (00:02:39)
Revealing mistake: When one of the staff of the Pokémon League goes over to type on the keyboard, she clips through a device in the process. (00:02:40)