In terms of Pixelmon, implementing this would most likely simply take the form of filtering your Pokedex search by biome instead of by Pokemon name. This would provide an easy and concise in-game way to check whether there was anything left to catch in a given biome, instead of looking up each Pokemon individually or having to rely on the wiki, which may have outdated or incomplete information.
In terms of Pixelmon, implementing this would most likely simply take the form of filtering your Pokedex search by biome instead of by Pokemon name. This would provide an easy and concise in-game way to check whether there was anything left to catch in a given biome, instead of looking up each Pokemon individually or having to rely on the wiki, which may have outdated or incomplete information.