The girl in the eastern house is looking to trade. She offers her Rhydon in exchange for a female Dragonair. The choice is yours, but a Dragonair's evolved form, Dragonite, will end up stronger than a Rhydon in the long run.
The Move Deleter resides in the house near the Poké Mart, and can help a Pokémon forget any of its moves. This is especially helpful for deleting HM moves, or moves that are exclusive to Generation II and cannot be traded through the Time Capsule.
Blackthorn Gym, 1F
Blackthorn Gym, 2F
BLACKTHORN CITY POKéMON GYM LEADER: CLAIR
The Blessed User of Dragon POKéMON
The Blackthorn Gym is devoted to Dragon-type Pokémon. Dragons take less damage from Grass, Fire, Water, and Electric moves, and are only vulnerable to Dragon- and Ice-type attacks. Almost any Pokémon caught in Ice Path will do well here. Reaching the Gym Leader requires dropping boulders from the floor above to form a path, so bring along a Pokémon that knows Strength.
Take the stairs to the second floor and head to the southeast corner to find two boulders; move the right one to the south wall, and the left one up to reach the break in the floor. Go to the northeast corner and drop the last boulder through the hole. Take the eastern stairs down to the center platform and beat the last two Cooltrainers to reach Clair.
Each of Clair's three Dragonair can paralyze an opponent with Thunder Wave, while her Kingdra can potentially do the same with DragonBreath. Use status ailments to your advantage, and replenish your health often so you are not caught off-guard by Kingdra's Hyper Beam.
Clair refuses to accept defeat. She claims that you are still not ready for the Pokémon League, and tells you to take the "dragon user challenge". She informs you of the Dragon's Den, a large cave located under the city, and tells you to retrieve the Dragon Fang from there to be accepted as a true dragon user. Only then will she give up the Rising Badge. Bring along a Pokémon with Surf and Whirlpool, and cross the lake behind the Gym.
Climb the ladder down to the main cavern. Surf to the southwest and use Whirlpool to calm the waters. Continue east behind the shrine and step onto the second strip of land to find the Dragon Fang. Clair appears and grudgingly hands over the Rising Badge, which makes all Pokémon obey regardless of level and enables the use of Waterfall in the field. She also gives you TM24 (DragonBreath).
Upon leaving the cave, Elm calls and asks that you visit him at the Lab. Traveling to the Pokémon League requires passing through New Bark Town anyway, so rest up and head south to reach Route 45.
Route 45 is a rugged route leading down from the mountains. The path splits and recombines multiple times, and many small cliffs prevent northbound travel. The east entrance to Dark Cave is located just outside of the city, and the route eventually reaches a small lake, where it turns west toward Route 46.
Turn right and surf south across the lake. Grab the Revive on the southeast platform, and go west along the water's edge to find TM13 (Snore). Surf north and go west along the platform. Make a U-turn to reach the northwest corner; the man here will give you the BlackGlasses, an item that enhances Dark-type attacks. Head south and jump the two ledges to reach the opening to the Violet side.
Surf to the west and jump the ledge to get a Potion if you didn't already. Go south and use Rock Smash to proceed eastward. Smash another rock and loop around the northeast corner to find a Hyper Potion. Jump the ledge and head south to find a Full Heal. Continue south to reach the Route 45 exit.
The rugged mountain road of Route 45 comes to an end in Route 46, as the mountains give way to smaller cliffs. To the west, a small grove of Berry trees grows in a secluded field. Head south to the gate, and cut through Route 29 to return home to New Bark Town.