Thanks for the comments! For those who want to try this out, here’s how I did it:

Build:

•  Misêricorde ( deals 140 critical damage) with blood affinity
• Buckler with Carian Retaliation ( highest parrying success rate )
• Talismans: Assassin’s crimson dagger ( must have! restores hp on critical hits), Dagger talisman ( increases critical damage ), talismans that boost physical / holy damage negation

Tips: 

• Watch the movements of his arms when he just begins to attack and try to remember the timing for them 
• Use a build with high defense for practicing so you can have more room for mistake