>>32402948Get your favourite Pokémon in the earliest possible game and collect the ribbons you like for it while transferring it to newer games.
It doesn't need to start in Gen 3 but that would be ideal. If your favourite is from Gen 5 then so be it, there are ribbons for it to collect in Gen 6 and 7 anyway. You also don't need to restrict yourself to one Pokémon, you can do it with as many as you like.
You also don't need to collect ribbons that you don't like. There is no prize or acknowledgement for having all ribbons and it isn't possible since there are numerous time-limited and unreleased ones anyway.