You go to cinnabar island then go inside the Pokemon mansion. Press A at every pokeball u find.
Get the key from the basement of the mansion next to the gym.
its inside the mansion
You have to go to the old mansion beside the gym and get a key
If you mean, "how do I unlock the Gym where he is", you have to go into the mansion and get to the basement. There you will find the key to open the Gym
The basement.
you must find the key to the cinnabar island gym......
You get the card key which lets you open the gym which is locked.
u can find it in Pokemon mansion.
Explore the ruined mansion to find the key.
You get the card key which lets you open the gym which is locked.
you have to go into the old haunted mansion in order to get the key for the gym
get the key in the od mansion on cinabargo to cinnibar island, then go in that place next to the gym and look for secret key. then get out and then you can go in the gym in cinabar island