None yet! I have to re-watch all my old VCR tapes to find mistakes. Or, send me any you find.
The First Movie- The Pidgeot of the Cooltrainer who flew him to New Island is incorrectly called a Pidgeotto by its owner.
Team Rocket mistakes a Scyther sillouhette for an Alakazam. How could they? It was noted in the commentary for the movie that this was on purpose, to show not everyone knew everything about Pokemon.
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Pokemon 2000- In the opening short, in the Dance of the Bellossom, a Poliwhirl joining in the festivity says 'Poliwrath' instead of 'Poliwhirl'.
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Lucario and the Mystery of Mew- When Mew transforms into a Pidgeot and flies away with Meowth and Pikachu, Kidd Summers calls it a pidgeon. Though it technically is a pidgeon, she may also have mis-pronounced it PI-jit.
As this page is obviously not a complete reference yet, please e-mail me at pkmnmaster22@hotmail.com with any you've seen or know. Just tell me the season, episode name, and the particular mistake made by dubbers. I'll post them ASAP and with credit.