A few common ones:
>thinking rock was immune to electric because a lot of rock types are/were also ground
>thinking shiny butterfree was pink back in gen 2 because of that one episode and no comprehensive internet encyclopedia to look up all the new recolors
>thinking groudon was ground/fire because magma is hot
>thinking the whirl islands were supposed to be the orange islands because of the 2nd movie and lugia was there
>all the mewthree/pokegod rumors
>thinking the tcg had attack/defense mode like yugioh because a lot of the cards referenced attacking/defending pokemon and nobody knew how to play because the rulebook only came with full decks and was above most kids' reading levels
