After you defeat Clemont and get the Voltage Badge, Trevor asks you to go to Route 14, Laverre Nature Trail.
After you and Trevor compare Pokédexes, your neighbor challenges you to a pokémon battle. He has a level 35 Meowstic, a level 37 Chesnaught, and a level 35 Absol.
After the battle, Shauna and Tierno arrive. Shauna wants to go together to the scary house that is rumored to exist near Laverre City. Your neighbor decides not to go, but the rest of your friends go north to visit the scary house.
Look behind the swing set to find a Rare Candy. You can use this item on a pokémon to make it increase by one level instantly.
In the middle of the sandbox on the left, there is a hidden Super Potion. Use your Dowsing Machine if you have trouble finding it.
When you're ready, go north where your friends went.
In the tall grass, you can find Skorupi, Weepinbell. Less commonly, you can find Karrablast, Quagsire, Carnivine, Goomy, and Shelmet. Very rarely, you can find Haunter. You can find all of those pokémon except for Skorupi and Weepinbell if you walk on puddles, and you can also find Stunfisk on puddles. Fishing with the Old Rod, you'll find Poliwag. With the Good Rod, you can find Barboach and Poliwhirl. You might also have horde encounters with Bellsprout, Ekans, and Skorupi.
There is some water to the north that you can walk into. Use your Dowsing Machine there to find a Tiny Mushroom on some leaves.
Near the leaves with the hidden Tiny Mushroom, you find Pokémon Ranger Melina, who has a level 35 Arbok and a level 37 Pyroar.
Go east through the grass and then north. You find a Cleanse Tag. If you give it to your lead pokémon, you will be less likely to encounter pokémon of a lower level than your lead pokémon.
Now go west past Pokémon Ranger Melina. To the west, you can see an item. You have to south into the water to reach it. It's a Big Mushroom.
Go north from there. You'll encounter Pokémon Ranger Nash. He has a level 38 Goomy.
Go east and across the grass. You encounter Hex Maniac Anina. She has a level 34 Litwick and a level 34 Haunter.
Go east from the Hex Maniac and then north through the grass. There is a Pokémon Ranger running around the stumps to the north. He is Pokémon Ranger Reed. He has a level 35 Poliwhirl, a level 34 Loudred, and a level 36 Fraxure.
Go west from the Pokémon Ranger who is running around. There is a Hyper Potion in the water.
There is a Hex Maniac to the north who doesn't battle you, but instead gives you TM06 Toxic. Use Surf to go north from her. In the water, check on the spinning red item to find a Damp Rock. If you give it to a pokémon that knows Rain Dance, the effects of Rain Dance will last for eight turns rather than five.
Go east from the girl who gave you the TM to find Fairy Tale Girl Imogen. She has a level 33 Floette and a level 35 Slurpuff. There is Roseli Berry tree east of her.
If you have Cut, use it on the prickly tree south of the Fairy Tale Girl to find TM61 Will-O-Wisp.
Go west. Shauna will come toward you. You and your friends will go into the house. The old man there will tell you a scary story then ask you to give him a tip, saying that if you don't, you might see something really scary. It's your choice.
Afterward you will all go outside. Go south from the scary house. Turn on your Dowsing Machine to find a hidden Revive on a gravestone-shaped rock on the right side of the watery path. Go south of there to find a Spell Tag.
Now go north to reach Laverre City.