Solved Merc and immunity question

Hi all. I can't find information about that. I'm with f sorc, merc act2 without infinity. When he hit immune to fire monster or any other and I join hitting that monster die faster. What merc do? Decreasing def?

 

Hello & Welcome @erontron

Stats; be it Defense/Offense or Attribute Decreasing or Increasing Effects will only occur IF your Merc wears specific Items.
Such as Infinity, Insight, etc. etc.

The only thing your so to say NAKED Act 2 Merc will provide you is his own Aura. (Check below)
Basically, he only does Physical damage. You do not profit of it until he's properly geared.

For Normal, and Hell Difficulties:

• Combat - Prayer
• Defensive - Defiance
• Offensive - Blessed Aim

For Nightmare Difficulty:

• Combat - Thorns
• Defense - Holy Freeze
• Offensive - Might