How to defeat the boss of the Ice Barrows Duengon?

So I am having considerable trouble beating Theorick and I wondered if it might be my build? (I am a level 50 Acrobat Assassin currently but have only completed content to around 43-45)

I created a WynnBuilder build but realized I can't post links so this is my build:

Helmet: Enhanced Assassins Hood
Chestplate: Springtrap
Leggings: Diminution
Boots: Giant Step
Ring 1: Sticky Decoder Ring
Ring 2: Concentration
Bracelet: Vindicator
Necklace: Durum's Serenity
Weapon: Influence


My Skill Points (without gear) are:

Strength: 19
Dexterity: 19
Intelligence: 16
Defense: 23
Agility: 21

Please help.