* Grodon is a Pokémon from the third generation (Hoenn region). Pokemon Diamond is from the fourth generation (Sinnoh region).
* Grodon is an exclusive Pokémon to Pokémon Ruby and Sapphire. It can be found on Route 134 and can evolve from a Swampert.
If you're looking for a similar water-type Pokémon in Diamond, you can try catching:
* Gyarados: Evolves from Magikarp, which can be found in various water locations.
* Floatzel: Evolves from Buizel, which can be found on Route 204.
* Lumineon: Can be found in various water locations.
If you really want a Grodon, you can try trading with someone who has Pokémon Ruby or Sapphire.