Serpentbone Blade is a Katana in Elden Ring. The Serpentbone Blade scales primarily with Strength and Dexterity and is a good Weapon for high Dexterity characters to engage in mid-range combat. It is capable of inflicting both Slash and Pierce attacks.

Serpentbone Blade Notes & Tips

• When Poison is procced on an enemy using this weapon, the resulting poison effect will deal double the damage per tick but last a third of the amount of time compared to poison procced by other means. This is referenced as "Lethal Poison" in the weapons description, but "Deadly Poison" in other weapons/items. Overall, Deadly Poison will do less damage than regular poison if both are left for their full duration. (Fetid Pot and Venomous Fang also have the same effect)
  • Its shortened duration can actually serve additional benefit; by reducing the uptime, it allows for more frequent triggers of certain damage boosting gear. The Mushroom Crown and the Kindred of Rot's Exultation can utilise this to great ends.
• Weapon Skill: Double Slash.
• This weapon cannot be infused with Ashes of War.
• Serpentbone Blade can be upgraded by using Smithing Stones.
• Causes Poison Buildup: 

   (66).

• Can't be enchanted with Magic nor boosted by Consumables.
• At 80 Dex, this weapon has an AR of 598 (294+304)
  • Compared to a Keen Uchigatana, which has an AR of 596 (258+337), the Serpentbone Blade has negligible higher damage, and deals more status effect (66 poison, vs 45 bleed).  Uchigatana maintains higher reach, but has lower base damage, so it only begins to outperform at higher levels.
• This weapon has a unique R2 that consists of a double slash.
  • The initial hit of the R2 comes out exceptionally fast, but does limited damage, useful for staggering lower poise enemies who will then be hit by the higher damage second attack.
  • Charging the attack causes your character to take a large step forward before delivering the double strike, making it a useful tool to close distance with dangerous enemies while still dealing considerable damage.
  • Because every weapons R2's normally counts as 2 hits towards "successive hits" talismans, AND this weapons R2 is a multi hit attack, this attack can make a single R2 allow you to gain 1 stack of all those talismans/items that boost the damage with successive attacks. (See examples below). This is because it takes a minimum of 3 hits to activate damage buff type "successive hits" talismans and one slash of the R2 counts as 2 hits while the one afterwards will count as a third hit. Whether the first or second slash counts as 2 hits is not known as of now.
  • The best setup to take advantage of the multi hit R2 is: Millicent's Prosthesis + Rotten Winged Sword Insignia (or the regular version if you don't plan to go into ng+ or having it dropped by another player) + Kindred of Rot's Exultation (if you can proc poison)+ Shard of Alexander (since the Skill is also a multi hit) and then Thorny Cracked Tear for your Flask of Wondrous Physick. 

Serpentbone Blade PVP Poise Damage Values in Elden Ring

Patch 1.10 adjusted PVP Poise Damage of all Weapons including some Spells and Incantations. Please take note that these adjustments are exclusive to PVP.