The Fourth Round Rumble - S1-E77
Character mistake: When a poster for the Pokémon League is seen, it misspells it as "Pokemon League." (00:20:22)
Mystery at the Lighthouse - S1-E13
Other mistake: When Brock turns his head to the costume, his nose is missing. (00:12:47)
Suggested correction: Agree with the other correction. Dropping details, such as facial features like a nose or mouth, and simplifying character designs is a very common and encouraged drawing/animation technique to imply distance. This isn't something the animators would just overlook. It was a deliberate decision. Ash and Misty similarly look somewhat less detailed than they do in closer shots. At best, this would be a deliberate mistake, but I personally think it falls under the umbrella of "suspension of disbelief" and shouldn't be considered a mistake given it's a stylistic choice to imply distance.
Suggested correction: His nose isn't seen because he is far away from the camera.
Island of the Giant Pokemon - S1-E17
Other mistake: In the recap, when Ash, Misty, and Brock are worried about the cyclone approaching, the edges of Meowth's ears are mistakenly colored tan instead of black. (00:01:16)
Other mistake: When Ash, Misty, and Brock are worried about the cyclone approaching, the edges of Meowth's ears are mistakenly colored tan instead of black. (00:20:08)
Tentacool and Tentacruel - S1-E19
Revealing mistake: When Brock says, "Ah! Zubat!" his neck is not fully colored in. (00:15:50)
Continuity mistake: When Brock says, "Looks like a greenhouse," he is holding the straps of his rucksack, but in the next shot, he is not. (00:04:08)
Who Gets to Keep Togepi? - S1-E48
Character mistake: At the beginning of the episode, the sign on the Pokémon Center misspells Pokémon Center as "Pokemon Center." (00:01:13)
Continuity mistake: When Misty asks if Brock knows how scared it makes her feel when he yells, the purple strap on her bag turns yellow like her shirt. (00:02:04)
Audio problem: After Jessie says that Team Rocket has to investigate, Meowth speaks, but his mouth does not move. (00:02:07)
Attack of the Prehistoric Pokemon - S1-E44
Continuity mistake: When Ash and his friends are surprised, Charmeleon starts evolving. The black straps on Brock's bag turn green like his vest. (00:15:44)
Continuity mistake: When Misty says that she and her friends have to go to Valencia Island, her bag disappears. This also happens at the end of the episode. (00:14:48 - 00:20:53)
The Path to the Pokemon League - S1-E8
Continuity mistake: When Misty says that she and Brock giving Ash the Badges was a mistake, the purple strap on her bag turns yellow, like her shirt. (00:02:11)
The Path to the Pokemon League - S1-E8
Continuity mistake: When Ash and his friends are standing in front of A.J.'s Gym, Ash's white sleeves turn blue. (00:02:45)
Continuity mistake: When Ash asks what Team Rocket is talking about, pads appear on Meowth's forepaws. (00:13:26)
Continuity mistake: When the Officer Jennys say that the news reporters are Team Rocket, Meowth's disguise disappears. (00:12:31)
Revealing mistake: As the camera pans up to Meowth in a crane, a building's windows move with the screen. (00:08:01)
Revealing mistake: When Team Rocket runs out of their cabin, Meowth's tail passes through a wall. (00:12:34)
Continuity mistake: When Daisy says that the Sensational Sisters have been performing for so long that they no longer get large crowds, Ash's left glove disappears. (00:04:38)
Attack of the Prehistoric Pokemon - S1-E44
Continuity mistake: When Jigglypuff notices that everyone fell asleep, Pikachu's tail changes from yellow with a brown base to brown with a yellow base. (00:18:24)
Attack of the Prehistoric Pokemon - S1-E44
Continuity mistake: When Ash says that Charmeleon still will not obey him, the green straps on his bag turn blue like his jacket. (00:11:06)