How to beat Pokémon Diamond with ONLY a Castform

Friday, July 25, 2025 

In this guide, you will learn how to beat Pokémon Diamond or Pearl with only Castform. And to anyone out there who has Platinum but not Diamond/Pearl, sorry to break it to you, but this guide will not work. Although the slow-bike tweak still works, and although you can still enter the Pokétch building in the void, Platinum fixed the code so you can no longer walk in the void without a “walk through walls” cheat from an Action Replay. I don’t want you to use Action Replay. This guide, for Diamond/Pearl only, can be followed the whole way through using only legitimate gameplay. No cheating, no hacking, no third-party modification software required. Without further ado, let’s do this.

Caution: If you have finished the main story on your copy of Pokémon Diamond or Pearl, and you care deeply about your file and can’t afford to delete it, buy or order a spare copy of Diamond or Pearl so you can play through the story on a new cartridge without sacrificing your important save file on your main cartridge.

• 1) Start a new adventure.
• 2) Play the game normally until you get a Pokédex from Sandgem Town.
• 3) After Dawn or Lucas gives you a tour of the town, go to the Poké Mart, then buy some Pokéballs.
• 4) Go back to Route 201, then catch two Bidoofs. Although you are not allowed to use this Bidoof in battle, you may need to use it for HMs, such as “Cut” and “Rock Smash.”
• 5) Go to the Pokémon Center in Sandgem Town.
• 6) Go upstairs to the second floor. In the real world, grab your other DS or 3DS, then trade one of your Bidoofs for an egg containing a Castform.
  • If you don’t already have a Castform egg, you can make one by leaving Castform in the Daycare with a Ditto.
• 7) After you make this trade, your team now consists of your starter, a Bidoof, and an unborn Castform. Walk around until the egg hatches.
• 8) After the egg hatches, switch-train your newborn Castform against wild Pokémon until the Castform reaches Level 7. From this point on, Castform is the only Pokémon you are allowed to use in battle.
• 9) Defeat Gym Leader Roark to get the Coal Badge.
• 10) Play the game until you reach Eterna City.
• 11) Defeat Gym Leader Gardenia to get the Forest Badge.
• 12) Go to the Team Galactic building, then defeat Commander Jupiter to rescue the owner of the bike shop.
• 13) Go to the bike shop to get a bicycle.
• 14) Get the Explorer Kit.
• 15) Cycle down Route 206, then go back to Jubilife City.
• 16) Go to the left lamppost near the Route 202 entrance to Jubilife City.
• 17) Change your bike to the “slow” gear, then ride, without interruption, four steps east and a step south. This L-shaped movement has now tricked the game into loading the graphics of Route 203 onto part of Jubilife City.
• 18) Enter the Pokétch Building.
• 19) Press “Down” to enter the void just below the entrance.
• 20) Walk 17 steps west, then 14 steps north.
• 21) Walk 63 steps west or until you see the words “Veilstone Store” at the top of your screen.
• 22) Save the game, then close and reboot the game.
• 23) After reloading your game, press “Left” to go a step west. The game now thinks you are at the Pokémon League, and you will hear the music of that location.
• 24) Save the game, close, reboot.
• 25) After reloading your game, press the Up button, and the game now thinks you are in the “Hall of Fame.”
• 26) Amusingly enough, Rowan and Cynthia are now talking to you in the void. Congratulations! You have finished Pokémon Diamond with a team of only a single Castform.
• 27) (Optional) It’s also funny as the game shows your team. As far as the game is concerned, you somehow defeated Cynthia and her powerful, famously challenging team, including a famous Level 66 Garchomp, all using only a Level 25 Castform! Share this moment with your siblings or friends, and you can show them that you “defeated” Cynthia with only a Level 25 Castform.

• [ ] —  e.g. December 31, 1999
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