Adamantine Longsword
The Adamantine Longsword is a rare, versatile melee weapon crafted at the Adamantine Forge in Grymforge. It deals slashing damage, ignores enemy slashing resistance, and applies Reeling to struck targets.
Key Takeaways
The Adamantine Longsword is a forge-crafted versatile weapon whose value comes from its resistance-piercing property and its Reeling effect, rather than from unusually large base damage.
Forge-crafted Underdark weapon
You obtain the Adamantine Longsword by using a Longsword Mould and Mithral Ore at the Adamantine Forge in Grymforge, after dealing with the forge’s guardian, Grym.
Versatile slashing damage
The weapon deals 1d8 slashing damage in one hand or 1d10 when used two-handed, so its damage profile changes with the wielding mode.
Its main offensive property ignores slashing resistance
Lethal Weapon allows the sword to ignore enemy resistance to slashing damage, giving it a specific advantage against resistant targets.
Reeling rewards either wielding mode
A hit applies Reeling for one turn when the sword is wielded one-handed and for two turns when it is wielded two-handed.
It is not universally optimal for every wielder
The sword remains a martial longsword, so characters without the appropriate weapon proficiency may not be able to use its attacks and weapon actions effectively.
Compared with an ordinary longsword
Its primary distinction is the package of Lethal Weapon, Diamondsbane, and Reeling; the choice is therefore about those properties and the forge opportunity, not just the longsword damage dice.
Overview
The Adamantine Longsword is a rare, versatile melee weapon in Baldur's Gate 3, defined less by raw damage than by its interaction with slashing resistance, objects, and the Reeling condition. It is a crafted Act 1 progression reward from the Adamantine Forge rather than a normal vendor weapon.
As a longsword, it can be used in one or both hands and changes its practical role accordingly. Its defining property, Lethal Weapon, lets its slashing attacks ignore enemy resistance to slashing damage. That makes the sword particularly relevant when an otherwise ordinary physical attack would be reduced, while leaving the choice of wielder, proficiency, and broader class setup to the player rather than prescribing a single build.
Diamondsbane gives the weapon a separate niche against objects by making attacks against them automatic critical hits. This is not a general critical-hit bonus against creatures, so the sword should not be treated as a universal replacement for weapons built around critical-hit chance. Its value is instead divided between a conditional environmental utility and a combat property that matters when slashing resistance is part of the target's defenses.
The Adamantine Longsword also applies Reeling when it hits a creature: the condition lasts for one turn when the sword is wielded one-handed and two turns when wielded two-handed. That difference gives the two-handed mode a more pronounced control-oriented identity, while the one-handed mode leaves room for an off-hand item. The weapon therefore offers a meaningful handling choice beyond simply selecting the larger damage die.
It occupies an early-to-mid-game place in Baldur's Gate 3's equipment progression and is obtained through the Adamantine Forge in the Grymforge area of the Underdark. It competes with other longswords and with named weapons that may offer stronger enchantments, elemental riders, or build-specific effects, but its resistance bypass and Reeling application give it a distinct purpose. The weapon is part of the base game rather than a separate DLC or variant item, and its usefulness depends on whether those mechanics address the encounters and targets in the player's current Act 1 route.
Statistics
This game publishes dice damage rather than 0–100 bars, so the verified damage, enchantment, weight and value are listed instead. Taken from the project's verified weapons database, not from generated text.
- Base Damage1d8+1
- Damage TypeSlashing
- Enchantment+1
- RarityRare
- Weight1.35 kg
- Value100 gp
- Entry TypeNamed / special
Figures verified against Consolidated Game Weapons Database.
Compared to similar slashing weapons
| Weapon | Base Damage | Damage Type | Enchantment | Weight | Value |
|---|---|---|---|---|---|
| Adamantine Longsword | 1d8+1 | Slashing | +1 | 1.35 kg | 100 gp |
| Phalar Aluve | 1d8+1 | Slashing | +1 | 1.35 kg | 250 gp |
| Adamantine Scimitar | 1d6+1 | Slashing | +1 | 1.35 kg | 190 gp |
| Duke Ravengard's Longsword | 1d8+1 | Slashing | +1 | 1.35 kg | 250 gp |
| Justiciar's Scimitar | 1d6+2 | Slashing | +2 | 1.35 kg | 480 gp |
Damage is the dice expression; weight and value are the game’s own figures. From Consolidated Game Weapons Database.
How to Obtain
- Baldur's Gate 3, Act 1; the Adamantine Forge is in Grymforge, in the Underdark.
- Access to Grymforge and the Ancient Forge area.
- One Longsword Mould and one piece of Mithral Ore.
- The Grym forge encounter must be completed before the forge can produce the weapon.
- The weapon is not a vendor item, ordinary enemy drop, or DLC/NG+ reward.
- 01Travel to Grymforge in the Underdark during Act 1 and reach the Adamantine Forge. The forge is in the Ancient Forge area, beyond the Grymforge exploration route; no vendor, boss drop, or quest reward provides this weapon directly.
- 02Collect the Longsword Mould from the mould found in the Adamantine Forge area, then obtain a piece of Mithral Ore from the ore deposits in Grymforge. The mould and ore are separate required components.
- 03Place the Longsword Mould in the Mould Chamber and the Mithral Ore in the Crucible at the Adamantine Forge. Operate the forge and defeat Grym when the forge encounter is triggered; after the encounter, operate the forge again to complete the crafting process and receive the Adamantine Longsword.
- 04The result is a guaranteed Adamantine Longsword when the Longsword Mould and Mithral Ore are used successfully. The Longsword Mould is unique, so this specific weapon can normally be crafted only once per playthrough; other Mithral Ore can instead be used for a different Adamantine item.
Availability
Requires Reach the Adamantine Forge in Grymforge, obtain the Longsword Mould and Mithral Ore, and defeat Grym to complete the forge encounter.
The Adamantine Longsword is not a vendor-stock item and has no purchase price; its availability is tied to the Act 1 Adamantine Forge progression. No separate DLC, Online, difficulty, or NG+ version is listed.
Mechanics and Handling
The Adamantine Longsword is a versatile weapon whose main mechanical distinction is not a new attack sequence, but the way its properties affect resistant targets and objects. Its normal longsword attacks use slashing damage and can be made one-handed or two-handed, changing the weapon’s damage die from 1d8 to 1d10. The choice also changes the duration of its Reeling effect.
As a melee weapon, it relies on ordinary attack positioning rather than a charge, draw, ammunition, or reload cycle. Its practical handling is therefore determined by reach, action economy, and whether the wielder wants the one-handed or two-handed version of its versatile attack. The sword does not require a separate resource to maintain its special properties.
Versatile attacks and Reeling
Wielding the sword in one hand preserves access to its 1d8 longsword damage and applies Reeling for one turn when an attack hits. Using it in both hands changes the weapon to its 1d10 damage mode and extends the applied Reeling duration to two turns. The longer duration makes the two-handed mode more useful when the wielder can afford to give up a shield or other off-hand option.
Reeling is a combat condition rather than a separate damage effect. It makes the struck target less reliable at attacking while the condition lasts; the two-handed version gives that disruption more time to matter. Because the effect is tied to a successful hit, it is most valuable when the wielder can consistently connect with attacks rather than when the sword is being used only for occasional opportunity attacks.
Lethal Weapon against resistance
Lethal Weapon allows the Adamantine Longsword to ignore enemy resistance to slashing damage. This matters when a target would normally reduce incoming slashing damage through resistance: the sword’s slashing attacks are not reduced by that resistance. The property does not turn every attack into a critical hit, does not replace the weapon’s normal damage type, and should not be treated as a general solution to other forms of damage mitigation.
The effect is especially relevant for a martial character who expects to keep making weapon attacks against varied enemies. It is less distinctive when the target has no slashing resistance in the first place, so the sword’s advantage is encounter-dependent rather than a permanent increase to every attack.
Diamondsbane and weapon actions
Diamondsbane causes the sword’s attacks against objects to be automatic critical hits. This is a narrow utility property: it applies to objects rather than ordinary creature targets, so it should not be read as a universal critical-hit mechanic. When interacting with a destructible object is the immediate problem, the property gives the sword a specific advantage over a normal longsword.
The weapon also provides the standard longsword actions Pommel Strike, Lacerate, and Rush Attack. These actions give the wielder options beyond the normal attack sequence: Pommel Strike provides a close-range bonus-action attack option, Lacerate adds a damaging weapon manoeuvre, and Rush Attack lets the user close distance while attacking. They are standard longsword capabilities rather than Adamantine Longsword-exclusive skills, so the sword’s unique handling remains centred on Lethal Weapon, Diamondsbane, and the variable Reeling duration.
No durability or ammunition management
The Adamantine Longsword has no ammunition, magazine, reload, or durability loop to manage. Its special properties remain available whenever the weapon is equipped, and its combat decisions are instead governed by positioning, action economy, the one-handed or two-handed grip, and whether the target’s resistance makes Lethal Weapon relevant.
Upgrades and Variants
Strengths, Weaknesses and Best Uses
Strengths
- Lethal Weapon lets the sword ignore enemy resistance to slashing damage, preserving its slashing damage against resistant targets rather than requiring a different damage type.
- Diamondsbane guarantees critical hits when the weapon strikes objects, giving it a specific advantage in encounters or interactions where objects are valid targets.
- Its versatile property supports either one-handed or two-handed use, allowing the wielder to adapt between retaining an off-hand item and using the larger two-handed damage die.
- The weapon applies Reeling on hit: for one-handed use the condition lasts one turn, while two-handed use extends it to two turns.
Weaknesses
- Its resistance-bypassing advantage is specific to slashing resistance; it does not by itself address resistance to other damage types.
- The weapon's most distinctive effects are matchup-dependent. Diamondsbane matters when striking objects, while Lethal Weapon matters when the target resists slashing damage.
- Forging it requires the Longsword Mould and Mithral Ore at the Adamantine Forge, as well as defeating Grym, so obtaining it demands a substantial Underdark crafting route rather than an ordinary pickup.
- Choosing the two-handed mode for the larger damage die means giving up the flexibility of a one-handed weapon with an off-hand item; choosing one-handed instead gives the shorter Reeling duration.
Best uses
- Use it against enemies whose slashing resistance would otherwise reduce a longsword's damage, particularly when the character is already committed to slashing melee attacks.
- Use it as an early-to-mid-game versatile frontline weapon when the party can reach the Adamantine Forge and wants a crafted reward with resistance-ignoring utility.
- Use the one-handed configuration when an off-hand item is more important than the longer Reeling duration.
- Use the two-handed configuration when extending Reeling from one turn to two turns is more valuable than retaining an off-hand item, or when the wielder wants the weapon's two-handed damage option.
- Keep Diamondsbane in mind for encounters involving objects, where its guaranteed critical-hit behavior is relevant.
Compared With Similar Weapons
| Weapon | Class and damage dice | Enchantment | Distinctive effect | Best comparison point |
|---|---|---|---|---|
| Adamantine Longsword | Not stated in the available evidence | Diamondsbane automatically critically hits objects; Lethal Weapon ignores slashing resistance; applies Reeling for 1 turn one-handed or 2 turns two-handed | A versatile anti-resistant weapon with utility against objects and a reliable Reeling rider | — |
| Phalar Aluve | +1 | Provides the Sing and Shriek weapon actions, offering party support or an offensive debuff role | A stronger choice when its unique team-wide utility matters more than resistance bypass | — |
| Longsword | No enchantment bonus | Standard longsword weapon actions without the Adamantine Longsword's unique passives | The baseline for judging whether the Adamantine weapon's forge investment and special effects are worthwhile | — |
| The Blood of Lathander | +3 | Lathander's Light, Lathander's Blessing, and access to Sunbeam | A realistic adjacent alternative for characters prioritising high enchantment, undead protection, and radiant utility over longsword reach and slashing effects | — |
Trivia
- The Adamantine Longsword’s Diamondsbane property is specifically tied to object targets: attacks against objects automatically score critical hits. This gives the weapon a distinct utility interaction outside ordinary creature combat.