This Chapter is only exploring two dungeons, and meeting two Legendary Pokémon. Also, Bidoof dispatches from your team, so you don't have to baby him anymore. Before entering the next dungeon, though, Pikachu will notice a shiny red gem on the ground. It's got to be worth a lot of money. Now you'll head into Thick Fog Forest!
You better train a bit before going to the next dungeon. Just keep traversing the dungeon, which isn't too hard. It's too easy, actually. Eventually, you'll hit the end.
Pikachu will find a big statue in the ground ahead of you. You'll examine it, and Pikachu will tell you it's a Groudon, the legendary Pokémon of the land. You'll remember the shiny red gem you found earlier, and you and Pikachu will put the gem in a hollow in the statue. That's a lot of money down the drain. Oh, well, it will open up a new dungeon for you to explore! Who needs money when you have a new dungeon to explore anyway!
This dungeon is pretty challenging, considering there's no real theme to this dungeon type-wise, it's almost like random. Just keep going through, using the save point midway, and eventually you'll reach a Groudon.
This boss fight can get pretty intense, so you have 4 options:
After you choose your course of action, utilize it. Sometimes, it tends to try to attack and jump away, so attack it with Geo Pebbles or something when it does that. Also, try to use Water or Grass attacks on it. After a few dozen hits, it will go down.
The Groudon will disappear, and you'll enter a cave with Uxie inside. Don't worry, you don't have to battle it. Yet. It will tell you about the Time Gear and a bandit called Grovyle, and basically he's trying to use the Time Gears for a special mission he has so far succeeded in, and you have to stop him. After more talking, you'll go back to Treasure Town, and begin Chapter Ten!