That’s only in the Kanto and National Pokedex. In the Johto Dex, #20 is Furret. In the Hoenn Dex, it’s Lombre. In the Sinnoh Dex, it’s Abra. In the Unova Dex, it’s Simisear. And in the current generation, #20 is Scatterbug.
Wait a minute. That’s 6 Pokemon…
I think I know what must be done…