Mistralton Cave 1F
As soon as you enter, you'll notice how dark this cave is. Have one of your Pokemon use Flash (obtained from Castelia City ) to light up the cave. Once you can see a little better, move south from the entrance. You'll see a boulder here
Use Strength to push it two tiles east first (if you push it south, you'll get it stuck and have to exit and re-enter the cave to reset its position), then push it two tiles south into the hole. Move over it and down the steps to your south. Head east and you'll be stopped by a Hiker looking for a battle.
Trainer Battle: Hiker
Once he's been busted, trudge further east and push the next boulder east into the next hole. Continue east until you reach the Veteran guarding a doorway. He'll tell you that you can't head through the doorway until you've beaten the Pokemon League . Instead, head north up the stairs.
You should see some steps leading down to a lower area to your east. Move down them and collect the Dusk Ball there. Head back up the stairs and head west. You'll see another Hiker there. Take him on!
Trainer Battle: Hiker
Now move west along the strip of land north of the stairs. There's an item here. Grab it to find that it's a Yellow Shard , then head west along the strip of land south of the stairs. Make sure you have your Dowsing MCHN switched on and use it to find the Super Repel here.
If you want, you can now head west down the stairs and push the boulder into the hole. You then have a quick way to exit the dungeon in the future. Once you've down then, head back up the stairs and move south-west. You'll notice a set of stairs leading up onto the second floor.
Mistralton Cave 2F
Once you enter this floor you can head two directions: north or east. Let's first head north, as there's really only one thing to do there. You'll almost immediately come upon an Ace Trainer clearly looking to get destroyed by some amazing Pokemon Trainer, eh?
Trainer Battle: Ace Trainer
Now go back south and down the stairs to the east. Move down to the boulder to your south. Push it east using Strength until it falls into the hole. Move over it. Now move past the stairs taking you north and head east. When you reach the end of the path, you'll see a nearby rock, sitting all alone.
Walk over to it and check it to find that it contains a Green Shard . Fancy that! Head back and move up the stairs. Head east until you reach the stairs leading back down. Move down them, then head south and move up the stairs taking you west.
Head south down to the south wall of the cave and follow the path west until you reach an item. Collect it to find that it's a Hyper Potion . Backtrack and move back down the stairs. Now head north, past the stairs that you came from until you reach another Ace Trainer. Time to take her on too!
Trainer Battle: Ace Trainer
Now go north past the Ace Trainer and up the stairs. Move along to the end of the path and grab the Blue Shard . Once you have it, backtrack to the stairs, move down them and follow the thin path just to the left of the stairs around until you reach a point where there's a path leading south and a short path leading west.
Turn your Dowsing MCHN on and head down the west path. At the end of it is a hidden Ultra Ball , so be sure to collect it. Once again, backtrack all the way back to the stairs ( don't head south and jump over the ledge). Now move back south of the Ace Trainer to the boulder.
Push it west, into the hole. Move over it and head west. When you reach the next boulder, do the same and push it into the hole. You can now head back to the entrance to this floor easily, or you can move up the stairs to the third and final floor, back east a little. Do so!
Mistralton Cave 3F
Okay, first head down the stairs taking you west and head west until you're in the very bottom-left corner of the room. In the rock relaxing here is a Full Heal . Check it to grab it, then move back up the steps to the entrance. This time, head east. First move around the stairs leading north, taking the path north around them instead
At the end is an item with your name on it. Grab it to find that it's TM80 - Rock Slide ! Backtrack to those steps that you just bypassed and move up them. Grab the Escape Rope on the platform here, then continue north and head down the stairs taking you west.
Move north and take the next set of steps taking you west. From there, immediately move south down to the boulder. Use Strength to push it into the hole. Push the other boulder south into its hole, then move up the steps taking you west. You'll see an old fella here.
Speak with him if you want, then head down the thin path directly behind him. Check the rock at the end to find a Dragon Gem . Head back to the old man. If you take the path leading north along the western wall, you'll find an empty area. Originally, Cobalion resided here, but no longer does. That's all there is to do!
You can either use that Escape Rope that you found earlier to exit the cave back to Route 6 , or you can manually take the shortcuts that you've created by pushing some of the boulders into holes all the way back to the entrance.
If you were heading to Chargestone Cave Part 2 , skip back to that section, find where you were and continue on. If not, skip back to wherever you were in the plot or feel free to head wherever.