Pokémon Diamond and Pearl/Mt. Coronet (north)

'''Mt Coronet is massive and it's split into a northern and southern section. Mt Coronet also has a strong magnetic field inside it which is needed to evolve your Nosepass and Magneton into Probopass and Magnezone respectively, just level them up in here and they will evolve. You will be in the northern section as you accessed the mountain through Route 211. You can find the elusive Feebas in the basement of this section. This section leads to Route 216 when you exit on 1F2.'''

Before coming into Mt Coronet make sure you are stocked up in Healing/Restore items as the trek ahead of you can be brutal and it's a long way to a rest stop/town.

1F 1
When you first enter Mt. Coronet through either side of Route 211 you will be on 1F 1. The Pokémon are relatively weak and you should have caught them already at some point of the game. There are some items here to collect. In the boulder directly east of the Eterna City exit is a hidden Revive. the breakable rock to the east and push the boulder to the north then follow the path to find TM69. Jump of the ledge and head east. The rock on the wall before the next boulder has a hidden Elixir on it. Push the boulder to the east and go all the way to the wall then south to find an Escape Rope. Go north and you will see the exit to Celestic Town but don't go outside. On a rock to the west of this exit above a ledge is a hidden TinyMushroom. Go back east and then go north to push the boulder. Break the rocks to the west and you will find a Rare Candy at the end. Head back east and follow the path north and at the end will be stairs to go down to B1F. On the rock right before the stairs to B1F is another hidden TinyMushroom.

Pokémon found

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Items

 * Revive(hidden) - on a rock east of Eterna City exit
 * TM69 Rock Polish - north of Revive
 * Elixir(hidden) - on rock on wall before 2nd boulder
 * Escape Rope - south of Celestic Town exit
 * TinyMushroom(hidden) - on a rock west of Celestic Town exit
 * Rare Candy - past the breakable rocks north of Celestic Town exit
 * TinyMushroom(hidden) - on rock next to stairs to B1F

B1F
The basement is the only spot to catch a feebas which will be told more in depth in another section on this page.

Upon arrival you will be surrounded by fog. Just use Defog and you can see clearly now. Break the rock to the west and pick up the Stardust. On the rock directly south of the Stardust is a hidden Nugget. Go north and go down the second stairs then go north and push the boulder and further down is a Soft Sand. Go back to the stairs that you past and go down them then go all the way to the end. Smash the last rock then go on that spot and click on the wall to the north to find a hidden PP Up. Surf to the island in the middle of the lake and you find a Light Clay. Surf to the northeast corner of the lake and you'll find a Max Elixir. Go west and break the rock and on the middle rock between the stairs is a hidden Ultra Ball. Go up to the stairs to the east and push the boulder to get the Revive. Follow the path east and use Rock Smash when needed. At the end of the path is a Full Restore. Follow the path back up and go down the stairs and go up the next stairs then go north. On the southern rock in the northwest corner is a hidden Rare Candy.

The next part of this guide is going to go over catching a Feebas but if you want to skip this the take the exit in the northwest corner to go to 1F 2.

Catching Feebas
Feebas can be caught while fishing in the lake. It will appear on 4 random tiles and those tiles change each day. It doesn't matter which rod you use as if you find a Feebas spot there will always be a 50% to encounter it. You can also still find other Pokémon in the Feebas tile so it's important to at least fish 4 or 5 times in each tile to make sure it doesn't have a Feebas. This can be a very slow process and it can take a whole day. Once you find a Feebas tile then it's recommended to catch multiple ones if you are playing other Gen 4 games or use record mixing on the same day you find the tile that way the other game has the same tile as you. When you are fishing it is recommended to use a Max Repel so you don't encounter Pokémon while surfing.Surfing. Once you caught as many Feebas as you went then hop out of the lake and go to the exit in the northwest corner and head to 1F 2.

Pokémon found

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Items

 * Stardust - west of the southern exit
 * Nugget(hidden) - on a rock directly south of the Stardust
 * Soft Sand - down second stairs from southern exit and at the end of the path
 * PP Up(hidden) - down first stairs from southern exit against northern wall above a breakable rock
 * Light Clay - on island in middle of the lake
 * Max Elixir - northeast corner of lake
 * Ultra Ball(hidden) - on middle rock between stairs north of lake
 * Revive - behind boulder to the east of the Ultra Ball
 * Full Restore - at end of path east of Revive
 * Rare Candy(hidden) - northwest corner on southernmost rock.

1F 2
A pretty small room and there is only a hidden HP Up in the wall between the two rocks in the northeast corner. To the west you will see the light out of the mountain but dont be to excited as you will see your first glimpse of snow in the game. Time to bundle up and enjoy the winter wonder routes of Sinnoh starting with Route 216.

Pokémon found

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Items

 * HP Up(hidden) - northeast corner in wall between the two rocks