Antspur Rapier — Best Overall Scarlet Rot Weapon

Requirements: Strength - 10 / Dexterity - 20
The Antspur Rapier remains the best all-around weapon for a dedicated Scarlet Rot build.
It combines innate Scarlet Rot buildup with the speed of a Thrusting Sword, allowing it to apply Rot much more safely and consistently than the slower heavy Rot weapons.
Its biggest advantage, however, is customization. Unlike many status weapons, the Antspur Rapier can change its Ash of War and affinity while retaining its innate Scarlet Rot.
This creates several possibilities. You can optimize its regular weapon damage, add Poison or Blood Loss, or use an Ash of War that complements the rest of your setup. This makes Antspur capable of applying multiple status effects without sacrificing its core Scarlet Rot identity.
Its fast thrusting attacks also work extremely well with Pierce counterattack bonuses and successive-attack effects.
If you want one weapon around which to build a complete Scarlet Rot character, Antspur Rapier is the safest recommendation.
Location: Dropped by Maleigh Marais, Shaded Castle Castellan, west of the Shaded Castle in Altus Plateau.
Poleblade of the Bud — Best DLC Scarlet Rot Weapon

Requirements: Strength - 14 / Dexterity - 22 / Arcane - 20
The Poleblade of the Bud is the most significant dedicated Scarlet Rot weapon added in Shadow of the Erdtree and provides a completely different alternative to Antspur Rapier.
This Halberd scales with Strength, Dexterity, and Arcane and comes with the Unique Skill Romina's Purification. The Skill launches the player into a graceful sequence of sweeping attacks surrounded by scarlet butterflies, dealing damage while applying Scarlet Rot.
Unlike Antspur, the Poleblade cannot change its Skill or affinity, so there is considerably less build customization. It instead functions as a complete weapon built specifically around its unique moveset and Skill.
Arcane is an important offensive attribute for the Poleblade because of the weapon's own scaling. However, its Scarlet Rot buildup itself should not be treated as something that simply continues scaling with Arcane.
Its biggest disadvantage is availability. You obtain it after defeating Romina relatively late in Shadow of the Erdtree, making it primarily an endgame, DLC, or NG+ build-around weapon.
Location: Obtained by trading the Remembrance of the Saint of the Bud with Finger Reader Enia.
Rotten Battle Hammer — Best Strength Scarlet Rot Weapon

Requirements: Strength - 26 / Dexterity - 8
The Rotten Battle Hammer is the strongest choice for players who want to combine Scarlet Rot with a traditional Strength playstyle.
It provides innate Scarlet Rot buildup alongside Strike damage and strong stance damage, giving it advantages that faster Rot weapons such as Antspur Rapier don't have.
More importantly, it can change its Ash of War and affinity. This allows the weapon to be optimized around Strength while retaining its innate Scarlet Rot, or incorporated into more specialized status setups.
Its slower attacks mean it generally takes longer to apply Rot than the Antspur Rapier, but in return you gain substantially more damage and stance pressure per hit.
Location: Dropped by the Rotten Duelist west of the Consecrated Snowfield Site of Grace.
Rotten Greataxe — Best Colossal Scarlet Rot Weapon

Requirements: Strength - 30 / Dexterity - 10
The Rotten Greataxe provides Scarlet Rot on a Colossal Weapon, combining status buildup with powerful individual attacks and high stance damage.
Interestingly, the weapon isn't restricted to a pure Strength setup. Its default scaling favors Dexterity more than its appearance might suggest, while customizable affinities allow it to support different attribute distributions.
Compared with faster weapons, applying Scarlet Rot requires more commitment because each attack is significantly slower. However, you aren't dependent on Rot for damage: the weapon can still punish enemies with powerful regular and Heavy Attacks while the status builds in the background.
This makes it a strong option for players who want Scarlet Rot to complement a heavy melee build rather than define every attack.
Location: Dropped by the Rotten Duelist northwest of Ordina, Liturgical Town, in the Consecrated Snowfield.
Scorpion's Stinger — Best Fast Pure Rot Weapon

Requirements: Strength - 6 / Dexterity - 12
The Scorpion's Stinger is a dedicated Scarlet Rot Dagger that trades Antspur's customization for an extremely fast and lightweight moveset.
Its rapid attacks make it capable of building Scarlet Rot quickly when you can remain close to an enemy. It also requires very little attribute investment, making it easy to incorporate into Dexterity-focused setups.
However, it has two significant weaknesses: very short range and no affinity/Ash of War customization.
For most builds, Antspur Rapier provides more flexibility and better reach, but Scorpion's Stinger remains a strong option when rapid close-range status application is the priority.
Location: Found inside the Grand Cloister after crossing the Lake of Rot.
Honorable Mentions
Rotten Crystal Spear

A Spear with innate Scarlet Rot that provides significantly better reach than most Rot weapons. However, its awkward Strength/Dexterity/Intelligence requirements, fixed Skill, and lack of customization make it harder to recommend as the centerpiece of a dedicated build.
Rotten Crystal Sword

The Rotten Crystal Sword combines innate Scarlet Rot with Magic damage, but its fixed Skill and mixed scaling make it less flexible than Antspur Rapier. It can still work well for characters that already meet its Intelligence requirement.
Rotten Staff

A massive Colossal Weapon with innate Scarlet Rot and extremely high Strength requirements. Its slow attack speed makes status application inconsistent compared with faster Rot weapons, but it can be fun for a dedicated heavy Rot setup.
Rotten Crystal Staff

Despite its name, this is primarily a Glintstone Staff rather than a practical Scarlet Rot weapon. It can technically inflict Rot by physically striking enemies with the staff, but that isn't a realistic reason to build around it. Its real purpose is spellcasting, so it shouldn't be treated as one of the main Rot weapons.