As soon as you enter, Clyde will be blown towards you and will then give you some Fresh Water.
You'd better like running, because you're going to have to outspeed some very fast fans in this Gym! The wind will blow every couple of seconds, and it will knock you backwards towards the entrance unless you happen to be safe behind some walls (you'll see green tiles on the floor beneath you if you are).
Blow Me Away!
In order to outspeed the wind, you're going to need to make sure you run by holding in B. Running is very important to move quickly enough to make it to the next areas before the wind blows you around.
From the start, wait for the wind to blow, then run on over to the safe area to the east. You're going to want to run to the north and fight the Pilot. He's got a Swoobat L37. After beating him, quickly run in front of the safe area. The wind will knock you against the back of it.
You need to run north as soon as the wind dies down and get over to the safe area up there. Wait for the wind to die down again, then run south and to the safe area to the west.
From there, you've gotta run a little south and then over west. Once the wind dies down, make a break towards the southwest. There's a Pilot down south you can fight that has a Sigilyph L37.
You're really going to have to make a run for it to get to this next spot! Run north from the Pilot and then quickly head east. There's a shelter there. Wait for the wind to blow, then hurry on over west and north. Fight the Pilot in there, who uses an Archen L36 and an Unfezant L36.
You probably won't be able to get to the next point, because there's a lot of swerving, but it's ok if you get caught in the wind; you'll land right by a Pilot, and he'll fight you with his Unfezant L37.
Alright, run over to the green shelter and get ready for one heck of a run. You're going to have to run north and then west quite quickly. Make the run for it, then run north as quickly as you can! You should hopefully make it to the next shelter just fine.
Now you'll have to choose between three paths. The top and middle one lead to dead ends, so if you want to skip running into a Pilot, you'll have to take the bottom path. The Pilot has a Ducklett L36 and a Swoobat L36.
From here, just head over to the east, wait for the wind to die down, then run north until you reach the red area. Now you're in the clear! Heal up your Pokemon, then get ready to fight against the sixth Gym Leader, Skyla!
Her Pokemon are all part Flying-type and typically have a lot of Speed. This can make them a pain to fight if you're using slower Pokemon.
She leads with her Swoobat, which packs Acrobatics and can hit for some pretty hefty damage if you're unprepared. It also has Heart Stamp and Attract to annoy you with.
Her Skarmory is a rather interesting Pokemon. It's a Steel/Flying-type, giving it a whole ton of resistances and immunities, plus it has a whole ton of Defense. Special-based attacks are the only way to go against it, but since it has Sturdy, you won't even be able to take it out in one hit. Its attacks aren't too threatening, but Steel Wing can hit pretty hard if you're not expecting it. Use Fire- or Electric-type attacks against it for a sure bet, but Water- and Rock-type attacks also work pretty well, particularly Special-based ones.
Lastly, she has her Swanna, which is a Water/Flying-type swan Pokemon, in case you couldn't tell. It likes to use Agility to speed it up substantially, then use BubbleBeam or Steel Wing to hit any Rock-type Pokemon looking to take advantage of its weakness, or just use Air Slash against anything else to hopefully force you to flinch.
You probably don't have any Ice-type Pokemon, but if you did, her Steel-type attacks would be a good counter for them.
After beating her, she'll give you the Jet Badge, which ensures traded Pokemon up to level 70 will obey you. Additionally, she'll give you the powerful TM62 (Acrobatics), which is a 55 power Physical-based Flying-type attack — however, its power doubles if you have no held item equipped, making it an awesome 110 power Flying-type attack capable of doing a lot of damage at the cost of losing your held item. A lot of non-Flying-type Pokemon can learn it, too!
Whenever you're ready to leave, just step south of her and prepare to get blown straight out the door!
Once you're outside, Skyla will appear behind you and ask where Professor Juniper is. She'll show up and says she needs to get to Opelucid City, but Twist Mountain is inaccessible, so she suggests coming in from Lentimas Town. Well, that sounds great!
Before doing anything else, though, make sure you go over and talk to the kid inside of the house above the Pokemon Center. He'll notice your Jet Badge and will tell you he hid an item. Go over to the southwest corner of the runway and then pick up TM40 (Aerial Ace), which is a 60 power Physical-based Flying-type attack that a whole ton of Pokemon can learn. It's not overly strong, but it's like Swift in the sense it has perfect accuracy. Neat! The kids will come over and congratulate you for finding the treasure, even allowing you to keep it. Cool.
Now, head into the airport and then talk to Skyla. She'll ask if you're ready to go. Well, are you ready? Are you ready to fly on a plane? Say Yes, and then... well, then Bianca shows up. She tells you about Reversal Mountain and decides to tag along. Great!
Why can't I fly?
If no one is inside of the airport waiting for you, you'll need to make sure that you've...
- Beaten the Gym Leader, Skyla, in the Mistralton Gym
- Talked to Professor Juniper in the first floor of the Celestial Tower
You'll need to do both of these things in order to fly over to Lentimas Town, so if you're running into problems, make sure you've done both of the above.
And just like that, you take to the skies and head over to the distant Lentimas Town!