Both are fast, aggressive assassin builds. Black Knife uses Faith for the %HP Blade of Death skill; Claw Assassin uses Arcane for bleed with rapid claw attacks. Different tools, same fantasy.
Black Knife Assassin
Boss killing with %HP damage
Strengths
- Blade of Death deals percentage HP damage
- Works against bleed-immune enemies
- Ranged projectile component on the skill
- HP reduction debuff on enemies
- Faith side allows healing incantations
Weaknesses
- Dagger range is very short
- Requires Faith investment alongside Dex
- Weapon is available late game
- Higher skill requirement
- Less flashy than claws
VS
Claw Assassin
Rapid bleed in PvP
Strengths
- Fastest attack speed of any weapon class
- Bleed procs extremely fast with dual claws
- Quickstep dodge is the fastest movement option
- Very flashy and satisfying gameplay
- Lower stat requirements
Weaknesses
- Extremely short range
- Bleed-immune enemies are hard counters
- Very squishy playstyle
- Outclassed by katanas in most scenarios
- D-tier for a reason
Verdict
Black Knife Assassin is strictly better for PvE — %HP damage works on everything. Claw Assassin is more fun for PvP with its blinding speed. For practical purposes, Black Knife is the superior assassin build.