It Is A Kecleon.
They let you see the invisible Pokemon (Kecleon) that is the blocking the way out of Fortree
From Steven at Fortree city. The thigh blocking you from going into the gym is an invisible Kecleon.
You have to find Steven and he'll give you Devon Scope and you use that on the invisible object.
It's an invisible Pokemon called Kecleon you can only reveal it with the Devon scope.
You must get the Devon Scope from Steven on Route 120, then you return and press 'A' when your reach the invisible barrier blocking your way to the gym. (Its actually a Keckleon in stealth)
its........................... cecleone!
In the route West of Fortree City, you will once again encounter Steven. He will give you the Devon Scope and you will subsequently be forced to challenge a Kecleon that is blocking the path across the bridge. Once either defeated or caught, the path will clear up. Use the Devon Scope on the invisible road block outside the Fortree City gym. A Kecleon will appear, however this time there is no battle; it will simply run away. The path to the gym is no open for you to pass through!
Fortree town is not a city or town in Platinium. Fortree town was a town on Ruby, Sapphire and Emerald.
Fortree City.
its in fortree city
fortree city
In Fortree City.