Did you ever mispronounce any Pokemon name as a kid, or any age I should say? Until you heard of the official pronunciation, do you move on to the official pronunciation or not? Here is some:
Mienshao - Before hearing the official pronunciation, I often pronounce it as "Mee-EN-shao". The official pronunciation is MEEN-shao, but I kept on pronouncing it as "Mee-EN-shao" 'cause the official pronunciation sounds a little... mean? Same applies for Mienfoo.
Deino line - The following official pronunciations for the Deino line are "DY-noh", "ZVY-los" and "Hy-DRA-gahn". I on the other hand, before hearing the official pronunciation, referred them as "DAY-noh", "ZWAY-los" and "HY-dray-gone". I pronounce 'em my own way, though.
Virizion - I was a little ticked with the official pronunciation, 'cause it isn't the same as Cobalion and Terrakion. The official pronunciation is "Ver-RAI-zee-on" when I rather call it "Vi-RIH-zee-on".
Braviary - I used to call Braviary "Bray-Vai-ree", until I heard the official pronunciation via Pokedex 3D Pro. Unlike the others above, though, I moved on and stared to pronounce it's official pronunciation "Bray-vee-air-ree"
Now for the most idiotic one...
Articuno - To tell you the truth, I always thought that Articuno was pronounced "Art-cor-nee-oh" as a kid. Even though the announcer of Pokemon Stadium clearly pronounces it's correctly, I have always thought that he pronounces it as "Art-cor-nee-oh". I wasn't that great at listening at that time.