I hired a nightmare act 2 holy freeze mercenary, however when I change difficulties using the same mercenary his aura changes to defiance. I don’t remember this being part of the original game and feel like it’s a bug. Confirmed this is happening to my friends as well.
Any additional info would be appreciated.
Ya they are supposed to permanently have those skills. I think they are just simply not mapped as separate hirelings like they are supposed to. They misunderstood how hirelings were supposed to work because this kind of mistake does not seem possible otherwise.
Hirelings are so imbalanced that it’s kinda a small issue anyway. I’d rather they put resources into fixing this last and fixing all of the other hirelings first. xD
Yes it is a bug. Super annoying.
Posting this in all the merc bug threads cause I dont see anyone else saying it.
If it helps to debug at all I am noticing that a normal Act 2 defensive merc (defiance) will show as Holy Freeze in his character sheet when in Nightmare, but he still casts defiance.
Yeah I figured something was going on. You’d think Blizz would have people working on d2r who understand the mechanics as well as we the players do so that this kind of crap doesn’t slip through the cracks.
Just a visual bug, the merc still uses the correct aura.
I just looked and yep, mine too - it’s defiance instead of holy freeze 
Mine is a little bit different scenario, but similar.
When a holy freeze mercenary goes to the Normal-difficulty game, the aura is correct (which is the holy freeze), but the skill-icon on the mercenary panel shows Defiance.
That’s correct aura, since you hired it in nightmare. The tooltip changes according to difficulty for some reason, but the aura remains the same.
It doesn’t always remain the same,
sometimes it does, sometimes the original aura is just not there.
Lemme remind you that blizzard is a young startup full of life.
And taking on Diablo II is a huge challenge for them.
Just be patient guys.
May I suggest you guys at blizzard get your hand on The good old “Kernighan & Ritchie” and seek for the chapter dedicated to act 2 mercenary implementation 
Haven’t seen it change once, merc is always using the same aura.
This is happening to me. I hired a Act 2 Normal difficulty Merc with Defiance, but now that I am playing in Nightmare difficulty, the same Merc is showing up as “Holy Freeze”. Blizzard please fix this!
I still need to check if it’s just a display icon bug, and that the Defiance aura still activates or not.
Update: Okay I just confirmed, even if the icon says “Holy Freeze”, my Merc still activates his original (Defiance) aura. I guess it’s just a visual bug, but works as expected.
It’s not often but sometimes you’ll see the aura is just not here at all.
And you get zero regen, be careful and you’ll spot it happening at some point.
However that is probably unrelated with the icon bug and is just another issue.
The game also crash sometimes I don’t remember Diablo 2 crashing so much.
That must be the resurrection, the brain might be damaged…
Maybe this is undead diablo 2 
omg can you trust the game ?
Maybe it’s gona bite you in the middle of the night ?
Any update on this being fixed? Same issue Merc was hired in Nightmare ( Might ) and displays Blessed aim when in hell. This is rather annoying.
You are wrong. It’s not visual.
Tested it in Hell with a Holy Freeze merc from Nightmare.
For some weird reason it took super long for the aura to activate, but even tho it says Defiance, it was in fact Holy Freeze with monster getting cold.
I gain no bonus Defense stats either.
Everytime i hop back on Normal difficulty the Merc displays defiance, but the second i hop back on Nightmare he displays Holy Freeze and casts Holy Freeze.
And even if he somehow manages to keep the Defiance when i get on nightmare, if he dies and i have to revive him. It’ll revive the merc with Holy Freeze.
Typical Blizzard, can’t seem to release games without everything bricking and falling apart.
Works fine for me, merc never changes his aura, only the tooltip changes when switched to another difficulty.
I had a merc with prayer and went to NM and it is now thorns. I noticed when I was not healing. So it is not just visual or saying the wrong aura. Not sure if thorns is even working but I know prayer is not happening.
Definitely having the same issue as you, Yumeria. My mercenary changed skills going from normal to nightmare, and from nightmare to hell. I didn’t realize it at first because I didn’t expect it to happen. But then after playing for about 5 minutes, I began to notice that I wasn’t as protected as I once was. That’s when I realized my hirelings abilities had changed, and couldn’t understand how or what happened to cause that.