|Carkol||Rock/Fire||Fixed - Along the tracks|
This is a dungeon that links together Routes 3 and 4. From the entrance, head north to begin with. You'll reach a slightly wider area with some wild Pokémon emerging from the ground. Go up and follow the minecart tracks west, then north after it bends. Along the left side, you should spot a mine worker posing for a battle. Search the ground to his right for a Revive.
Keith has a fairly rare Rock Pokémon that's native to these mines. If you're still learning type match-ups, Water, Grass, Ground or Fighting-types are the ones you want. That's a lot of weaknesses, but Rock has a lot of resistances too, to Normal and Fire to name a few.
After beating up Keith, continue left, then go all the way south. You'll reach an empty cave. Head through the short tunnel on the right to retrieve 3 Great Balls. Go back south, then exit the mine via the south. You'll be back on Route 3, but higher up. Grab TM54 Rock Blast next to the edge of the cliff. Then retrace your steps so you're back at the minecart tracks.
Follow the minecart tracks north. Soon, the tracks will bend towards the east. When this happens, there will be a female worker standing by a mine shaft entrance towards the top-left. You can avoid her by walking past when she's looking right.
That's a lot of Timburr! Granted, they are pretty common around these parts, but surely you could make a more diverse team... It's a Fighting-type, so Flying, Psychic or Fairy are ideal. Most likely, you only have Flying Pokémon though.
On the other side of her, there's an empty cave. Search the boxes along the top for some Stardust. Then grab TM26 Scary Face on the left. Now go back to the minecart tracks and follow it to the east, where it soon terminates. Ahead, there will be a wide cavern, with a bridge in the centre. Just before the bridge is another mine worker. Also, search the wall on the right for a Hard Stone.
Sandra's Pokémon are both moles found in the mines. They're also both Ground-types, so they share the same weakness: Water, Grass and Ice. Depending on the weather, you might not have any Ice-types, but surely you have some Water or Grass ones?
Walk across the bridge to the other side. Over here, there's a male worker towards the right. If you want to avoid a scrap, run past him when he's looking the other direction.
Russel continues the trend of owning a Pokémon you can catch in the current area. Rolycoly is a Rock-type and thus weak to Water, Grass, Ground and Fighting. You've no shortage of options.
Pick up the Heavy Duty Boots on Russel's right. Then go towards the left side of this area. Rummage through the boxes below the next set of minecart tracks for a hidden Ether. Then go up to the wheelbarrow and boxes to the right of the tracks to find a hidden Revive. Now follow the minecart tracks west. Soon, it will bend north. Grab the 2 Super Potions on the left.
Up ahead is the exit, but there's a dubious trainer standing at the end of the minecart tracks. Ensure your party is fighting fit, then proceed into the final area. As you step foot inside, you'll receive a warning. When have those ever worked on you?
Pokémon Trainer Bede
Bede appears to be a budding Psychic-type trainer. All of his Pokémon are Psychic and thus weak to Dark, Ghost and Bug. Dark-types like Nickit or Purrloin are recommended as they're immune to Psychic-type moves. Bug-types are good if they know Bug-type moves (like Bug Bite or Struggle Bug). Be wary as Solosis can use Endeavor to make your Pokémon have the same HP as it.
After trashing Bede, head north to exit the cave. Before leaving, inspect the boxes to the left of the exit to find some hidden Stardust.
A lot of rough Rock, Ground and Fighting-types here. Rolycoly is a new Rock-type Pokémon that can eventually evolve into the Rock and Fire-type Coalossal. As for the rest, if you need a Fighting-type, Timburr is a good shout out. There's also the Ground-type Drilbur, which can become the Ground and Steel Excadrill.