Assassin/Ninja Help I need help with creating a build

I’m currently level 49 Assassin, building toward an Acrobat-focused setup. I’m trying to recreate this gearset:

• Helmet: ShineSpark
  
  
• Chestplate: Marius’s Prison (currently missing)
  
  
• Pants: Winter’s Essence (I can farm this myself)
  
  
• Shoes: Durum’s Journey
  
  
• Weapon: Hashr Claw
  

The target stats from the build are (excluding armor bonuses in brackets):

• STR: 2 (+2)
  
  
• DEX: 28 (+2)
  
  
• INT: 32 (+13)
  
  
• DEF: 18 (+2)
  
  
• AGI: 18 (+10)
  

I’ve managed to get most of the pieces, but I can’t beat the boss that drops Marius’s Prison yet, I’ve tried but haven’t succeeded.

Before I can fully finish the build and improve my damage/survivability, I need a temporary replacement chestplate that will help me actually beat that boss so I can get Marius’s Prison.

Can anyone recommend a good substitute chestplate for an Acrobat Assassin around level 49, something that boosts damage, survivability, or mobility enough to help clear the boss fight?

Thanks in advance