Dreamyard

There are 2 trainers. 1 has 2 Purrloin Lv. 7, and the other has 2 Patrat and a Lillipup, all Lv. 7.

The person after the trainers will give you a Panpour if you chose Snivy, a Pansage if you chose Tepig, or a Pansear if you chose Oshawott. These are super effective against the Gym Leader's best Pokemon, so make sure you have an empty slot in your party. There's an X Defend right after, so grab that. Now head to the Gym!
GO TO STRIATON CITY
When you beat the Gym, come back here at the request of Fennel. Cut the tree in the way, and find Bianca. You go along, see a Muuna, then Team Plasma comes along to get that Dream Mist stuff. Battle those Grunts! One has a Patrat and the other has a Purrloin, both Lv. 10. Then Ghetsis appears. In 2 spots! Then he teleports and disappears. What's up? Turns out it was a Muusharna. Fennel runs up, grabs a Poke Ball, and runs off.
In the grass you can find a Muuna. There are a few items. Grab 'em and head to Route 3.
GO TO ROUTE 3