How I Unlock the Harpoon Gun—and Why It Won't Fire on Land

Quick Answer

I unlock the Harpoon Gun by finding Horsetail around the Bridge side of Skunk Pond and analyzing it.

The Harpoon Gun is a Tier 3 Stabbing weapon with this recipe:

1 Sunken Bone

• 2 Horsetail Stem

• 2 Eelgrass Strand

Unlocking the recipe is only the first gate. If I cannot dig the Sunken Bone or cut Eelgrass yet, I fix the relevant Omni Tool upgrade before doing another resource run.

I also unlock Harpoon Bolts before leaving base.

And if the finished Harpoon Gun appears completely broken when I try to test it on dry ground, I stop troubleshooting:

the Harpoon Gun only works underwater.

The Harpoon Gun initially sent me looking for a much more complicated unlock than the one I actually needed.

Because it is an underwater Tier 3 weapon, I expected the recipe to come from:

• a deep Pond facility;
• a boss;
• an Optical Disc;
• or some late Ominent progression.

Instead, the material that finally exposed the recipe was Horsetail.

Once I understood that, the problem changed from:

Where is the Harpoon Gun blueprint?

to:

Can I gather and process the three materials the recipe actually needs?

That is a much easier problem to solve.

I Look for Horsetail Around the Bridge Side of Skunk Pond

When the Harpoon Gun is my goal, I start around the Bridge side of Skunk Pond.

I do not dive toward the deepest section first.

Horsetail grows around this part of the new Pond region, so I work the vegetation near the Bridge and look for the distinctive plant among the other aquatic materials.

Once I have Horsetail, I leave the generic resource hunt alone.

I do not need a full inventory of every new plant just because I am already in the area.

I need to analyze the material that answers my current question.

Analyzing Horsetail Unlocks the Harpoon Gun

Simply collecting Horsetail is not enough.

I take it to a Resource Analyzer.

That is when the Harpoon Gun appears among the new recipes.

This is the first troubleshooting check I use if the recipe still seems to be missing.

If Horsetail is sitting in my inventory but the Harpoon Gun is not showing up, I ask:

Did I actually analyze the Horsetail?

I do that before assuming the unlock is somewhere else.

The Harpoon Gun Is a Tier 3 Stabbing Weapon

The Content Data screen clears up several things at once.

The Harpoon Gun is:

Tier 3

and deals:

Stabbing damage.

It is also explicitly designed as an underwater weapon.

That information matters before I invest materials in it.

This is not a general ranged weapon that happens to be useful near the Pond.

I craft it because I specifically want a ranged option while fighting in the water.

The Exact Harpoon Gun Recipe

The recipe I use is:

1 × Sunken Bone

2 × Horsetail Stem

2 × Eelgrass Strand

This is where I stop doing generic Pond farming.

I check which ingredient is actually red in the recipe and solve that one.

If I already have enough Horsetail Stem, I stop collecting more Horsetail.

If Eelgrass Strand is finished, I leave Eelgrass alone.

If Sunken Bone is the missing material, I switch the trip around Bone.

That makes the weapon much faster to finish.

Sunken Bone Can Be a Tool Gate, Not a Location Problem

Sunken Bone was the ingredient that exposed another progression problem for me.

I could reach underwater areas containing the material.

That did not automatically mean my current digging progression was ready to harvest it.

If I can see a Bone resource but cannot collect it, I do not spend another ten minutes searching nearby for an easier version.

I check the Omni Shovel progression.

That distinction saves a lot of wasted exploration:

Visible resource + cannot harvest it = check the tool tier before checking another location.

I also prepare properly before a Bone run.

The deeper Pond is a bad place to arrive with:

• damaged equipment;
• almost no healing;
• a full inventory;
• or barely enough oxygen margin to get down and back.

If the trip is only for one missing Sunken Bone, I make it a targeted run.

Eelgrass Strand Can Be the Same Kind of Gate

The recipe also needs 2 Eelgrass Strand.

Again, finding the plant is only half the problem.

If I reach Eelgrass but cannot cut it, I stop treating that as a location issue.

The answer is the Omni Clippers progression.

Once the cutting function is ready for underwater plant life, I return and harvest the Eelgrass I already found.

That is one of the useful patterns in Into the Abyss:

I can often reach a resource before I own the tool that turns it into an ingredient.

When that happens, I remember the location and solve the tool first.

Horsetail Stem Is the Easy Ingredient Once I Know the Unlock

Compared with the other two ingredients, Horsetail Stem is straightforward.

The same Bridge-side resource that exposed the Harpoon Gun recipe also provides the stem material I need for the craft.

So I do not delay this part until the end.

When I first go after Horsetail, I collect enough to cover the 2 Horsetail Stem requirement as long as inventory space allows.

That means the return trip can focus on the harder underwater gates instead of making me repeat the easy plant run.

I Unlock Harpoon Bolts Before I Treat the Weapon as Finished

A crafted Harpoon Gun without ammunition does not solve my underwater ranged problem.

I also need Harpoon Bolts.

In my run, analyzing Koi Scale revealed the Harpoon Bolt recipe alongside other Pond equipment.

So if the gun recipe is already visible but Harpoon Bolts are still missing, I do not assume the gun unlock should have automatically included the ammunition.

I check whether I have analyzed the Pond materials I have been collecting, especially Koi Scale.

Once the bolt recipe is available, I craft enough ammunition for the trip I am actually planning.

I do not need to fill half my inventory with bolts.

I do want enough that the ranged weapon still has a purpose after the first few fights.

Why My Harpoon Gun Would Not Fire on Land

This was the easiest problem to misdiagnose.

I finally crafted the weapon.

I equipped it.

I tried to test it beside the base.

Nothing useful happened.

My first instinct was to wonder whether:

• I had the wrong ammunition selected;
• a control was broken;
• I had missed another upgrade;
• the weapon was bugged;
• or I needed to equip something else.

The answer was much simpler.

The Harpoon Gun only works underwater.

The Content Data screen already describes it as an underwater weapon.

I just ignored the practical meaning of that when I tried to test it immediately after crafting.

So if the Harpoon Gun will not fire on dry ground, I do not change keybinds or craft another stack of bolts.

I get in the water first.

I Test It on a Real Underwater Target

Once I enter the Pond, the weapon starts making sense.

Its main value for me is simple:

I finally have a ranged attack underwater.

That means I do not always have to close directly into melee range before I can start applying damage.

This is especially useful when I want to soften an enemy before committing to a closer fight.

It also gives me another option when a creature is occupying an awkward position around a deeper route.

I Still Carry a Melee Weapon and Shield

I do not build my entire underwater loadout around the Harpoon Gun.

Harpoon Bolts are finite.

Enemies still get into melee range.

Some Abyss spaces are tight enough that a ranged weapon is not automatically the best answer.

So on deeper runs I still like having:

• the Harpoon Gun;
• Harpoon Bolts;
• a reliable underwater melee weapon;
• a shield;
• healing;
• and light.

The Harpoon Gun gives me flexibility.

It does not replace everything else.

If I am already preparing for the main deep-water route, I combine it with the rest of my Into the Abyss loadout rather than treating the gun as a complete build by itself.

I Do Not Delay the Abyss Just to Perfect the Harpoon Gun

There is one more decision that matters.

Once I unlock a new Tier 3 weapon, it is tempting to:

upgrade it,

make more ammo,

test it,

upgrade it again,

and keep farming because the weapon feels unfinished.

I stop before that turns into another progression delay.

If:

• the Harpoon Gun is crafted;
• I have enough Harpoon Bolts for the next run;
• my main diving equipment is ready;
• and the rest of my loadout is repaired;

I move on.

I do not postpone the Diving Suit progression just because I want the Harpoon Gun to become the centerpiece of my build.

The Diving Suit removes the actual Abyss gate.

The Harpoon Gun gives me a better underwater ranged option after that gate is open.

Those are different priorities.

The Three Checks I Use When the Harpoon Gun Is Still Not Ready

By the time I know the route, almost every Harpoon Gun problem falls into one of three categories.

I have Horsetail but no Harpoon Gun recipe

I analyze the Horsetail.

I have the recipe but cannot craft the gun

I check the exact materials:

1 Sunken Bone + 2 Horsetail Stem + 2 Eelgrass Strand.

If one of those resources is visible but unharvestable, I check the related Omni Tool tier.

I crafted the gun but it will not fire

I stop testing it on land.

I enter the water.

That is the whole progression chain I use now:

find Horsetail

→ analyze it

→ check the Tier 3 recipe

→ solve the Bone or Eelgrass tool gate if necessary

→ unlock Harpoon Bolts

→ craft the gun and ammo

→ test it underwater

Once those pieces are in place, I stop troubleshooting and take the weapon where it was designed to be used.