I would change pretty much the ones that have largely similar color schemes/are just different shades of the same colors (Igglybuff/Jigglypuff/Wigglytuff, Meowth/Persian, Togepi/Togetic/Togekiss, Sunkern/Sunflora, Shellos/Gastrodon, Gible/Gabite/Garchomp, Carnivine, the monkeys, Basculin, etc.)...