Area: Haunted Cave

Name: Haunted Cave.
Location: Entrance in Route 110 and exit in Mauville City.
Area Type: Cave
Pokemon Found: Zubat (Lv 10-16), Sableye (Lv 11-16), Yamask (Lv 14-15) Shuppet (Lv 10-15), Gengar (Lv 20 (Only one per person that checks the tombstone at the middle)) Sandslash (Lv 13-18).
Landscape: Cave
Looks: A gloomy cave, filled with rocks at all the places and some cracks in the ceiling. This cracks are the only way that the sun enters and make the place a little bit illuminated. But, at night it gets really dark, so the person that enters the cave must have some way to light it up, as using Flash. But in the middle of the cave, not even sunlight gets in, and the darkness is increased by the Ghost Pokémon that lives in the cave.
Notable Places: A tombstone in the middle of the cave, that show the name of a Gengar.
History: This cave was used by kids to play a long time ago. But then, some guys appeared and wanted to hurt the kids. A Gengar helped them, and became a boy's Pokémon. The boy was really attached to the Gengar, and they played at the cave everyday. A group of bad Pokémons appeared and hurt the Gengar, the kid was so scared that run away. When he came back, he found the Gengar dead on the floor, so he buried him and put the tombstone in the cave so that the Gengar could rest in peace. But he didn't, and started haunting the place with the help of other ghost Pokémons.

Seems decent enough, approved unless otherwise stated ^^