How it works is there's a little button in the bottom-left corner of the Pokedex that says Habitat List. Touch that and then you'll be shown a list of the areas you've been to. Select any of them and not only will it show you where it is on the map of Unova, but it will also show little icons of the Pokemon you've encountered there on the bottom screen. Any that you've caught will have a little red Poke Ball stamp next to them, and if you catch all of the Pokemon in a route or area, you'll receive a stamp of approval for that area.On your way out of Floccesy Town, Bianca will stop you and then upgrade your Pokedex, allowing you to see what Pokemon are available in a route or area you've been to. It's the Habitat List feature. When she asks you if you need her to repeat what she just said, answer no, otherwise she'll keep talking.
Anyway, head on over to where the Hiker was on Route 20. He'll challenge you to a fight now that you have the Basic Badge. He uses a Riolu L11. After beating him, he'll let you through, though there's a Preschooler with a Psyduck L10 that stands in your way down the stairs.
When you walk past the Preschooler, Cheren and Hugh will show up. He'll show you the thick grass (also called dark grass), which tends to hold higher level Pokemon in it, but also has the potential to sometimes fight two Pokemon at once in a Double Battle inside it. He also gives you and Hugh some Pecha Berries, saying they'll be handy for the Virbank Gym, then heads back to his Gym.
|Route 20 (Spring/Autumn/Winter)|
|Pidove||/||Lv. 9 ~ 10||25%|
|Purrloin||Lv. 10 ~ 11||15%|
|Sewaddle||/||Lv. 11, 10||15%|
|Route 20 (Summer)|
|Sunkern||Lv. 9 ~ 11||26%|
|Purrloin||Lv. 10 ~ 11||14%|
|Sewaddle||/||Lv. 11, 10||15%|
As you can see, the Pokemon here are quite a bit stronger, plus you can find Venipede here, which turns into a pretty fierce Poison/Bug-type Pokemon if you give it enough of a chance to evolve it to its final form, Scolipede.
In addition to the Thick Grass, after you've gotten your first Gym Badge, you'll now be able to encounter rustling grass. Rustling grass is grass that is shaking and contains a rare Pokemon or an EXP-bearing Audino for you to fight. Only normal grass will shake, not thick grass, and the best way to run into shaking grass is to run back and forth a few squares away from a patch of grass. You'll be able to hear it shaking as well as see a single patch of grass shake. Make your way into it and fight the Pokemon inside!
|Route 20 (All Seasons)|
|Shaking Grass / Swirling Dust||Level(s)||Rarity|
|Audino||Lv. 2 ~ 4||90%|
If ever you need to do any training to raise your levels, the best way to do so is by running around outside the normal grass until you see it shake; odds are you're going to find an Audino inside, which gives a TON of EXP when you knock it out! It isn't too difficult to knock out, either, and makes for a wonderful source of EXP.
Always try to fight the highest level Audino you can in the most recent area to raise your EXP very quickly, and remember, it's ok to do switch training to help train two of your Pokemon at once by switching the weaker one you want to train out of the active slot in the first turn of the battle. That will split their EXP, although the weaker Pokemon will get a lot more EXP, due to it being at a lower level.
You can also find a Great Ball right next to Hugh in the Thick Grass, so be sure to pick that up, because it has a higher chance of catching Pokemon. Now head on over to the next Preschooler, who uses a Lillipup L10. Just past her is an Antidote. Over to the left of her is a Nursery Aide who uses a Dunsparce L11. Head up the stairs and pick up the Dire Hit and then fight the Twins, who use two Sunkern L9 against you in a Double Battle.
When you're ready, head on into the gate to go to Virbank City. As you enter, though, you'll be called over by the gate attendant and given a Great Ball.