after the blackthorn gymleader gets deafet she will ask you a favor i ziped through so i dont know what it was but the little pond behind the gym surf to the cave go to the left down there should be a whirlpool go acrost it go in the bottom of the building and answer the old guys question heartly and the gym leader comes rushing in she through a fit and the old dude will tell her to hand it over.
GET THE LAST BADGE......
To get the last gym badge you have to go to cinnabar island and you will meet blue. he will tell you that he will be waiting in veridian city to battle you. when you go to veridian city you go to the gym and fight him at the end of the gym.
in BLACKTHORN city (the last house)
After you get 3 badges (your last badge should have been the Relic Badge from Fantina in Hearthome City!), go to Jubilife City's Poketech Company Building and talk to the manager on the right of the main floor. He will give you the Marking Map.
You get it in Sootopolis city. If your playing Ruby or Sapphire. You would be fighting Wallace. In Emerald, You fight Juan.
The last gym badge is in viridian city for Kanto. For Johto it is in Blackthorn city.
GET THE LAST BADGE......
To get the last gym badge you have to go to cinnabar island and you will meet blue. he will tell you that he will be waiting in veridian city to battle you. when you go to veridian city you go to the gym and fight him at the end of the gym.
you have to get all of the other gym badges in kanto and then go to Cinnabarr island and talk to blue. then go to viridian city and go in the Pokemon gym!
in BLACKTHORN city (the last house)
viridian city
Go to Blackthorn city and beat the last gym leader.
In Sootolis city.
The last city in the Johto region is Blackthorn City. To get there, you must travel east from Mahogany Town. From there, you will see a cave (The Ice Path) in which you must go through to get there.
Viridian City.
sootopolis city
get the lendary pokemon lugia then you can go to blackthorn city and go from their