When you first enter Chargestone Cave, a couple of ninja dudes will surround you and escort you over to N, who is standing nearby. Then they'll disappear. N says that those guys were the Shadow Triad, whom Ghetsis hired to find out about you. N knows that Cheren is pursuing strength, and N feels that Bianca has reached the limit of her strength as a trainer, but he says that you seem to be neutral, which is why Ghetsis is interested in you. N warns that you will encounter Team Plasma up ahead. N goes farther into the cave.
After you head into the cave a little bit, Bianca and Professor Juniper will arrive. Bianca will tell you that some of the floating stones can be pushed. Professor Juniper will give you a Lucky Egg, which increases the amount of Exp that the pokémon holding it earns. The amount earned becomes the amount that it would get if it were boosted (i.e. if the pokémon were from a trade). Traded pokémon get even more EXP than before if they hold the Lucky Egg. In past games, this item was pretty rare, so it's great to get it so easily this time around!
As you go farther into the cave, you will find a crystal that won't move if you push it from the right. Push it from the left to move it out of the way. The floating crystals are attracted to the larger crystals that are embedded in the floor, so be sure to always push the floating crystals toward the large crystals.
When you walk past the crystals, some of the static will make sparks on you, but don't worry: it won't hurt you or your pokémon.
Chargestone Cave is a big place, and there are many trainers around. There are also some new pokémon here for you to catch:
With the types of pokémon that you will encounter, both wild and in trainer battles, I recommend that you bring a team of pokémon who know Ground, Fire, Fighting, Electric, and Grass moves. If you can, you should also fit some pokémon into your party that know Flying or Psychic, and Dark, Bug, or Ghost moves. One possible party that could work well here is Palpitoad, Liepard, Throh, Leavanny, Emolga, and Darumaka.
Buying Repels at the Driftveil Pokémart is a good idea, because Chargestone Cave is so big. Once you have caught the pokémon varieties here, and have trained up your pokémon as much as you feel like, go ahead and use the Repels to get a break from random encounters for a while.
Anyway, on the first floor, you will meet Scientist Ronald with an L29 Klink. Being a pure Steel pokémon, Klink is weak to Fire, Fighting, and Ground moves.
After the Scientist, go a little bit North to find Ace Trainer Jared, who has an L31 Archen. This is a Rock/Flying pokémon, so use Water, Electric, Ice, Rock, or Steel moves.
There is a hidden item to the northeast of the Ace Trainer. Nearby, there are a couple of floating crystals. Push the upper one to the left, and push the lower one down, to continue on.
After going down some stairs, you find another floating crystal. Push it to the right. Bianca and Professor Juniper will arrive and talk about the mysterious Klink.
To the north, you will find Hiker Hardy, who has an L26 Boldore and an L26 Gurdurr. Boldore is a Rock pokémon, so use Water, Grass, Fighting, or Ground. Gurdurr is a Fighting pokémon, so use Psychic or Flying moves.
A floating crystal blocks your path to the north, so continue south. Eventually you reach a wooden bridge, where the Shadow Triad will surround you and scurry across the bridge with you. Afterward, they will tell you that Team Plasma is waiting for you down some stairs ahead. Then they will disappear.
Get the Hyper Potion to the north, then push the floating crystal down to continue on. You will soon encounter Scientist Naoko, who has an L29 Klink. As before, use Fire, Fighting, and Ground moves.
The stairs are here, but before using them, go south of the stairs and push the lower floating crystal to the left, then continue left to find an Iron.
Down the stairs, you will find the Nugget brothers. Each of them will give you a Nugget. Hold on to these until you get to the Pokémon Center in Icirrus City, where a guy standing near the Nurse will buy Nuggets and other valuable items for twice the amount that you would get from selling them at the Pokémart.
To the west of the Nugget Brothers is a hidden Parlyz Heal, and some stairs leading up. Going up those stairs, you will find a narrow area to the south that has a hidden HP Up. If you hop down the ledge, you will be near the Route 6 exit of Chargestone Cave, so don't do that unless you want to backtrack. You'll be able to heal up in the cave soon, so keep that in mind if you're considering hopping down the ledge.
Returning to the downstairs area, go up the stairs to the right of the Nugget Brothers. There will be a couple of paths that you can take, but you should go to the right. Your Dowsing Machine will tip you off to a Revive hidden in the wall on the way. Farther along, you will find Doctor Wayne, who has an L29 Swadloon. Use Fire and Flying moves. After you defeat Doctor Wayne, he will heal up your pokémon for free whenever you talk to him. You're probably in need of this if you haven't used any repels.
Continue along this narrow path, then head west. Before fighting the Team Plasma Grunts, continue west and pick up the Timer Ball.
The first Grunt has an L26 Sandile, L26 Scraggy, and L26 Watchog. For the Sandile, use Water, Grass, Ice, Fighting, or Bug moves. For Scraggy, use Fighting and Flying moves. For Watchog, use Fighting moves.
The second Grunt has an L28 Scraggy. As before, use Fighting and Flying moves.
The next Grunt has an L27 Trubbish and an L27 Liepard. For the Trubbish, use Ground and Psychic moves. For the Liepard, use Fighting and Bug moves.
The next Grunt has three L26 Trubbish. As before, use Ground and Psychic moves.
After this is a Grunt who has an L27 Watchog and an L27 Sandile. For Watchog, use Fighting moves, and for Sandile, use Water, Grass, Ice, Fighting, or Bug moves.
Go west, down the stairs, and push the floating crystal to the left. Pick up the Thunderstone that is sitting in plain sight. Now go back, and push the other floating crystal up to get it out of the way.
The grunt here has an L28 Liepard. Use Fighting and Bug moves.
The other grunt nearby has an L27 Sandile and L27 Watchog. For Watchog, use Fighting moves, and for Sandile, use Water, Grass, Ice, Fighting, or Bug moves.
To the left are some stairs leading down. You will first encounter Ace Trainer Allison who has an L30 Drilbur and an L30 Zebstrika. For Drilbur, use Water, Grass, or Ice moves, and for Zebstrika, use Ground moves.
Push the floating crystal to the right in order to move it out of the way. Below, go to the right and then south to encounter Ace Trainer Stella. She has an L29 Gothita, an L29 Lilligant, and an L29 Ducklett. For Gothita, use Dark, Bug, or Ghost moves. For Lilligant, use Fire, Ice, Poison, Flying, or Bug moves. For Ducklett, use Electric moves.
To the left are some stairs leading down where you can get a Hyper Potion. Use the Dowsing Machine to find a Star Piece in the wall nearby. From here, go south through a narrow path, where you find a Rare Candy at the end. Go back the way you came, past the Ace Trainer, and head to the right. There is a Parlyz Heal to the south of the floating crystal, and you will find a BrightPowder to the north.
Now you can head back to the upper floor where you fought the Team Plasma Grunts. Go to the right and head up the stairs here.
On this upper floor, you will soon reach a place where you can go left, down, or right. Don't go right yet! N is waiting there and you'll have to fight him. Instead, explore the other parts of the cave and leave N for last.
To the west is Scientist Orville who has an L29 Klink. Use Fire, Fighting, or Ground moves.
Continue west, pushing the floating crystal out of the way, and check the wall near the crystal for a Max Potion.
Now go back to the area where you can go north, south, east, or west, and this time go south. You will encounter Ace Trainer Corky, who has an L30 Whimsicott and an L30 Tirtouga. For the Whimsicott, use Fire, Ice, Poison, Flying, or Bug moves, and for the Tirtouga, use Grass moves.
If you go south from the Ace Trainer, you will find a Magnet.
Now it's time to challenge N. Go north, then east, and he will be standing there. He will say that he finds it unacceptable that many different values and beliefs mix together to turn the world grey. Apparently he feels that his beliefs are the only ones that are right and he can't let anyone have other opinions. He also feels that pokémon and humans shouldn't be together. His dream is to keep pokémon away from humans so that pokémon can become perfect. Then he challenges you.
N has an L28 Boldore that knows Mud-Slap, Iron Defense, Smack Down, and Power Gem. Against these moves, Palpitoad would be a good choice, as would any pure Grass, Fighting, or Ground type. Scraggy, Deerling, Sandile, and Ferroseed are some dual typed pokémon that would also work well. Use Water, Grass, Fighting or Ground moves against Boldore.
N also has an L28 Ferroseed that knows Metal Claw, Pin Missile, Gyro Ball, and Iron Defense. Being a Steel/Grass pokémon, it is super-weak to Fire. If you chose Tepig as your starter and have evolved it into Pignite or Emboar, it has excellent defenses and attacks for Ferroseed. Otherwise, try sending out Pansear or Darumaka.
Another of N's pokémon is an L28 Joltik that knows Electroweb, Bug Bite, Gastro Acid, and Slash. It is weak to Ground attacks. Use Excadrill if you have one. Otherwise, use Drilbur or Palpitoad.
Finally, N has an L28 Klink that knows Gear Grind, ThunderShock, Bind, and Charge Beam. It's weak to Fire, Fighting, and Ground moves. Use Excadrill if you have one. If not, go for Palpitoad. As a last resort, Sandile or Drilbur will do.
After you defeat N here, he will express dismay at his defeat, and his hope to become friends with the legendary Pokémon. Bianca and Professor Juniper will show up. N will get all sassy with her and ask how she could possibly have no problems with the relationships that people have with pokémon. He hates the idea of categorizing pokémon and listing them in a pokédex, and demands to know what she has to say for herself.
She suggests that N let each person decide how to relate to pokémon, but of course N can't accept that since he wants everyone to get in line with his way of thinking. He thinks that people need to leave pokémon alone because people don't have a way to know if they are causing their pokémon to suffer. He refuses to tolerate a world where people might unwittingly be making pokémon suffer. After saying this, he leaves.
Professor Juniper expresses her hope that N will consider other people's feelings. She will go collect more data, because she believes that understanding pokémon will ensure that people don't make them suffer. Bianca goes with Professor Juniper, because Bianca is now her bodyguard. Now you can head on out to Mistralton City.