If you knew anything about video game graphics you would look at this post and laugh.
I meant 'just' in the sense of leaving it looking more or less the same, not to imply it would be easy. But if there is (inexplicable) demand for a retro-looking Pokemon game, then Nintendo have set the precedent of making pixelly graphics into cubey graphics, so why not do it to Pokemon?
If nothing else, it's bound to be more popular than Twinbee.
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"I'm Commander Shepard, and you're standing in the biggest library in Citadel Space. Look me up."