The Iron Maiden skill description is...lacking.
How much thorns? What exactly does this passive do?
As of patch 2.0.5.
Pre patch 2.0.5 information.
The passive gives you a static amount of thorns damage based on your current level and difficult level. You can't unlock Iron Maiden until level 50. And you can't unlock a passive slot until level 10.
Here is what i have so far:
Assuming level 70. And assuming a base value of thorns 6102 at normal level and level 70.
You can multiply that base value by the Monster Health % gained from the increase in difficulty level. And you will get numbers that are VERY close to the numbers that show up on the passive for each of those difficulty levels. The "calculated value" column in my picture is
Here are my numbers:
At level 70 the passive says the following for each difficulty level:
The tooltip on Blizzard's site is somewhat misleading. It's missing the X between the words, since it depends on your level. I just hit level 10 with my Crusader, and it says, "Gain 204 Thorns" damage. Not that I can select it, but that's what it says.
Levelling up to 11 didn't change that at all, so there's probably something else I'm missing. Perhaps it only starts increasing at a specific level.
Go to your game options, and turn on detailed tooltips. This will change the tool tips to describe precisely what the effect does. This is turned off by default, as the detailed tooltips are very technical, specifying things like "does 150% weapon damage as fire." In general, "thorns" seems to mean that any unit that attacks you takes damage. I infer this from my experiences where any equipment titled "of Thorns" or "Thorned" has a passive of "Ranged and Melee attackers take X damage."