The Goldenglow job, the first real quest of the Thieves Guild. You are supposed to get out to the island, clear Aringoth's safe, burn some of his bee hives. Killing him is not necessary, but okay if you have to.

I get in the house okay. I navigate to the stairs to access the upstairs. My character is level 24 or 25. Has a sneak of 71 and 1h of around 50. She has an orcish dagger of frost damaging (extra 3 or 4 damage). I poison it with a poison that does 25 damage. With the Backstab perk, I would think that this should be doing something like 35 x 15 = 525 damage right? I've never had any problems with backstabbing going wrong before. This toons HP are about 220 (non-buffed)

When I get to the stairs I find that a guard has a patrol up and down the halway at the base so I figure to be on the safe side I'll assassinate 'em, expecting htat he'll probably be standing right there at the base of the stairs when I'm on my way back.

I try to backstab him just as he turns to return down the hallway. I don't hear any nice KERCHLUNK from the backstab attack nor do I see any text, and the merc barely has a sliver of his health carved off . . . . WTF!?

Try again. Same thing.
Try again. Same thing.
Try again. Same thing . . .

Okay, so they've apparently got the mercs in this special mission scripted so that attempts to backstab them WILL fail?

http://www.uesp.net/wiki/Skyrim:Mercenary_(Goldenglow)

Well that sort of explains it now doesn't it? Mercenary (Goldenglow) HPs are:

50+(PC-1)×11.7
or in other words
50+(219)*11.7 = 3,147.3 HP

Great, so lets compare that with your garden-variety Skyrim Dragon . . .

http://www.uesp.net/wiki/Skyrim:Dragon

Legendary has 4363
Revered 3513
Standard ~1000

Ahh, that explains it. These are not just "Mercenaries," they are DRAGONBORNE Mercenaries!

DAAAMMMNNNN!!! That Aringoth is making some SERIOUS Septims on his honey! For Talos sake!? If either the Imperials or the Stormcloaks could get those eight mercs on their roster for a few weeks they could effectively win the war!

Oh but wait . . . thats not really the point. They aren't _really_ supposed to be Uber-Mercenaries, thats not part of the story per se. They are supposed to be just, 'stronger than your average city guard' type mercenaries (at least based on the dialoque), but with a twist. They are guarding a guy on a Thieves Guild mission where the writers want you to not kill anyone and do the mission as a "Thief" without any cross-training in "Assassinery"

So, the fact that the mercenaries are effectively unkillable has nothing really to do with any sense of the story or internal coherrence. The writers just don't want you to be able to kill them cause, well . . . somebody decided the Thieves Guild should be different from the Dark Brotherhood I suppose?

So, not only does your guild blather on about "not being assassins" and several guild mates moralize about deciding to 'not take lives,' but when you go to do your missions for them, you effectively have one choice: don't assassinate.

I would be perfectly fine with this sort of immersion breaking nonsense if they'd just put a big label on the Essential NPCs and the non-backstabbable mercs that says:

"DO NOT TRY TO KILL ME! THE WRITERS DID NOT WANT YOU TO KILL ME, SO I'VE BEEN GIVEN TWELVE TIMES YOUR HP"

I understand now why some people have been so incredibly negative on this game. It is frustrating that every time you get into the beauty of it, the open-endedness of it, the detail, the grandeur the artistry, the characters and their stories and you try to move forward on some quests, you find yourself back on a track where the 'appropriate choices' for your character to make have already been decided by the writers and if you want to finish that is what you better damn well do.

Well, I can see you put a lot of thought into your position/post on this, but honestly... I thought the Thieves Guild line was excellent from start to finish. I liked the variety of quests, I liked the twist and so on.

I know how games work under the hood rather well, but... eh. If I am enjoying a game, I enjoy it.

I was loving it too. Right up until my somewhat split second decision to assassinate that guard led me to look under the hood and realize that they were designed to be unkillable = there is one way to finish the quest, namely do not fight the mercs at all, or if you do, run away until they lose aggro and try again.

Assuming I still feel like playing that toon (well she didn't DIE per se, and I'm confident she can slip out of the house, so I guess it isn't a 'breach' of dead-is-dead) I'll just keep going and do what I'm supposed to do.

Its not that the whole game is frustrating like this; just that there are periodically these HIGHLY linear bits where the writers have funneled you into a 'no choice' path.

All TG02 mercs are templated on a Nord one-handed warrior who matches your level.

At level 24, they will have about 300 health. You're reading the formula wrong: PC is the player's level, not whatever number you're plugging in.

Okay. So how come I can routinely backstab assasinate City Guards, Imperials, Stormcloaks (maybe not bosses, but everything up to that) and I cannot kill these "mercenaries?" Moreover, when I've backstabbed bosses such as Bandit Chiefs (and this was like 10 levels ago) I'd take him down to less than 1/3 maybe even 1/4 of health in one hit (even with weak poisons).

Each repeated attempt to backstab that Goldenglow merc worked out the same: no sign that a full backstab bonus was applied (the toon has the X15 effect for back attacks with dagger and has one-shot killed many humans and criters that way) and only a sliver of their health gone, maybe 1/5 at most but probably more like 1/7.

Something is special about those mercs to make them effectively unkiillable or very, VERY difficult to kill anyway.

ADDIT redoing that formula with PC representing player level we get

50+(PC-1)×11.7
[50+ (24-1)]*11.7 = 73*11.7 = 854.1

Assuming my attack is 6 base + 3 cold + 25 poison = 34 total dam per hit X 15 for backstab attack, then I shoul've been doing about 510 damage in one hit.

Not sure how armor resistance, etc. plays into those backstab attacks.

But based on the fact that, instead of at least harming him badly---i.e., leaving him subject to die with just one more blow---he ws barely hurt AT ALL. We're talking he had at least 4/5th of his total hit points left, but probably more like 6/7ths left.

1. They're not unkillable, they're just REALLY tough. Which, at the outset of the mission, you're outright TOLD. You're also strongly advised AGAINST taking them on and told SPECIFICALLY that the best burglar in Skyrim, Vex, not only failed, but barely escaped with her life.

2. There are NO in-game means of determining number of hit points, just how hearty the adversary is. Meaning, all you are SUPPOSED to know, as the PC, is that these guys are really tough.

3. YOU destroyed your own immersion by NOT accepting the facts given to you and cheating out the reasons why they're so tough. IOW, it's your own fault you know the numbers, though hardly surprising given your emphasis on the numbers that followed. Skyrim is NOT for numbers geeks, that's for sure.

If I was effectively getting backstab bonus attacks on them, but just not finishing them off, I could go with your 'blame the user' response.

But assuming the backstab bonus, the observed loss ratios don't add up. At 854 HP and 510 dam in one hit, he should've been pretty near death; much as I've observed bosses are when I backstab attack them.

Instead, it was barely scratched. This suggests to me that there is something special about this mercs. They are resistant to backstabs, have high resists or something. Even if that was not the case, the fact that these "Mercenaries" seem to be the equivalent of eight Bandit Chiefs on steroids I find a bit over the top, and a clear sign that the quest designers wanted to railroad the player into a non-kill path to solve the quest.

I have found that I consistently have more fun just playing a game than looking at what's going on in the background. I'm not here to say your opinion is wrong or anything, since I know a lot of classical rpg players like seeing the numbers side. For me though, I just play the game and accept what I run into.

This was a mission that I felt fit right into Skyrim. A mission that we have never done before and different than a generic "Go here and retrieve X item." Sorry you formed a different opinion though.