The Deep Sea Scale can be a valuable item, but you’re only going to really need to use it for Clamperl in Pokémon Brilliant Diamond and Shining Pearl. After that, you use it to evolve Clamperl into Gorebyss. Here’s what you need to know about finding a Deep Sea Scale in Pokémon Brilliant Diamond and Shining Pearl.
We were able to find one while exploring the Grand Underground. You can reach the Grand Underground once you have an Explorer’s Kit, which you receive from the old man next to the Pokémon Center in Eterna City.
While down in the Grand Underground, you’ll have the chance to dig through fossil dig sites. These dig sites contain various rewards if you can remove them from the wall before the cave collapse, or you can unearth them before everything crumbles. There’s a lot of luck that has to do with finding a Deep Sea Scale this way.
We did find one in the snowy biome, in the Celestic Town Grand Underground region. You can reach this location if you use the Explorer’s Kit while in Celestic Town, which you can reach after you beat the fourth Gym Leader. You’ll gradually reach Celestic town by progressing through the story.