Happinas's Happy Nurse! - S3-E13
Character mistake: When Jessie asks if she can go to Pokémon Nurse School to become a nurse, the flyer she holds misspells Pokémon Nurse School as "Pokemon Nurse School." (00:07:53)

Revealing mistake: When Ash brings his first piece of meat into his mouth, another one disappears into thin air. (00:09:09)

Pokemon, I Choose You! - S1-E1
Continuity mistake: When Gary is first talking to his crowd, there is a woman with blue-green hair, a pink dress, and a yellow apron to the left, but in the next shot, she is replaced by a boy in a green shirt with brown hair and without an apron. (00:05:11)

Abra and the Psychic Showdown - S1-E22
Continuity mistake: When Ash notices the Saffron City Gym, the buildings in the background change. (00:06:38)

Character mistake: When first showing the tournament from the front, a sign misspells Pokémon Number One as "Pokemon Number One." (00:07:46)

Fushigidane and Fushigidane! Regaining the Monster Balls!! - S7-E34
Other mistake: The English title card misspells Poké Balls as "Pokéballs." (00:02:41)

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)

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: In her initial appearance, May is a little taller than Ash. In subsequent episodes, May is slightly shorter than him.
Continuity mistake: In one shot during Randall's flashback, the stripes on his shoes disappear. (00:09:22)
Continuity mistake: When Ash and Randall are about to attempt to break the pod Pikachu is in, Randall does not have his hat, but in the next shot, it appears. (00:17:27)
Continuity mistake: Before Ash, his friends, and the kindergartners throw their balls into the air, one of Ash's gloves disappears. (00:11:33)
Audio problem: After James says that Team Rocket should capture Sylveon, the sound of Wobbuffet's Poké Ball opening can be heard, despite him already being out. (00:06:27)
Giving Chase at the Rhyhorn Race! - S17-E7
Continuity mistake: When Ash and his friends look at the Rhyhorn, Ash's gloves turn completely black. This also happens when he puts on his uniform. (00:07:09 - 00:09:46)
Giving Chase at the Rhyhorn Race! - S17-E7
Continuity mistake: When Serena says that she wanted to meet Ash, the stripe on Ash's sleeve disappears. (00:05:16)
Flower Power - S3-E6
Audio problem: Towards the end of the episode, when Ash and his friends are cheering for Bailey, Misty's mouth moves, but no sound can be heard. (00:20:13)
Flower Power - S3-E6
Factual error: During the second battle with Team Rocket, Arbok and Victreebel use Tackle, a move they cannot legally learn in the games. (00:18:15)
Suggested correction: Differences between anime and games are not mistakes.