Larvitar is a Rock and Ground-type Pokemon available only in the Brilliant Diamond exclusive edition. You will find Larvitar in the main game as well as in the Grand Underground of Pokemon Brilliant Diamond & Shining Pearl (BDSP), but it’s locked to the post-game, and you do need to unlock the National Pokedex and Poke Radar. This guide shows how to reach the grand underground and the underground hideaway/ Biome where you will find Larvitar. You can find Larvitar in Route 207 as well as in the Grand Underground
How to unlock National Pokedex and Poke Radar
To be able to find Larvitar, first, you will need the National Pokedex and the Poke Radar. After finishing the Pokemon League, and registering all 150 Pokemon to the Sinnoh Pokedex, go and talk to Professor Oak in Sandgem town to get the National Pokedex and the Poke Radar.
Larvitar Location in Route 207 (Oreburgh City)
In Oreburgh City, head north onto Route 207 and go into a grassy area. You will find the grassy area on the left when you enter Route 207. There use the Poke Radar (obtained from Professor Oak) and then visit the spots where you see beeps in the grass. Repeat until you find a Larvitar.
Where to Find Larvitar in the Grand Underground
Read the article on How to reach the Grand Underground
There is a total of 18 hideaways/Biomes in the Grand Underground. You will find Larvitar in Rocky Cave, Big Bluff Cavern. These caverns can be identified on the minimap by their icon shown in the picture below. You will need to press ‘Y’ to open the minimap. Click here to see how to reach all the areas in the grand underground. Place Dragon-Type Statues in your secret base to increase the chances of Larvitar spawning.
Rocky Cave, Big Bluff Cavern (left to right)
Biomes mentioned above are highlighted below