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Christos: When you try to replace pokemon, not only must the pokemon file be 64x64 the sprite inside must be the EXACT same size as the pokemon you are replacing and must be positioned/centered the same way. Ex: mudkip is 40x41px (so your final sprite must be that small) that is what is causing your 'sprite too big' error. I had the same problem awhile ago. If you need more help importing, PM me if you wish.
... ok, i'll not Be a beta testa.... nyways, umm, hav u checked the tools showscase, i think there's some there, and there are sum tools too..... umm, i'll list when it squeezez into my head!!!