To get a Deep Sea Tooth in HeartGold/SoulSilver, you’ll need to head to Route 20 and use a Dowsing Machine to locate the hidden item. This item can be used to turn your Clamperl into a Huntail, or to raise its Special Attack.
But if you don’t have the Dowsing Machine (or if you just want to see the exact spot of the hidden item) then we’ll show that below!
DeepSeaTooth Location (Step-by-Step)
The fastest way to get to Route 20 is by flying to Cinnabar Island.
You’ll need both Fly and Surf to access the area.
And of course, you’ll also need Kanto unlocked too (so you’ve gotta beat the Johto E4 first).
Step 1: Head outside the Pokémon Center and use Surf on the water at the bottom of the island.
Step 2: Continue to surf along to the right, and you’ll find a long sandy island filled with trainers in the middle of the ocean.
Keep going right alongside that island.
Step 3: Eventually you’ll come across 2 caves on an island that’s totally surrounded by rocks.
Follow the rocks until you hit an end (blocked by rocks).
You’ll find your hidden Deep Sea Tooth there in the middle of the ocean (exact spot pictured below).
Note that this is the only location where you can get a Deep Sea Tooth in HeartGold and SoulSilver.
There are no wild Pokémon you can encounter that’ll be holding another one, and there are no other hidden locations either.
So if you really want more than 1 tooth (for whatever reason) then you’ll need to somehow trade one into your game from a different Gen IV game (specifically Diamond, Pearl, or Platinum).