Thinking about taking the dive...

[Fragbait]

IM works better with a Merc than Amp damage because every monster that attacks becomes injured, rather than every monster that the Merc attacks. By the time the first corpse drops, most of the group are at about half life or less.

Hi,

Figured since my fire golem / bone spirit necro is lvl 78, I'd throw my 2 cents in. This is meant for singleplayer only.

First, I'd like to support your above statement. Iron maiden is indeed a blast to play with - it just depends against which monsters...
Let's have us a look (hell difficulty):

Undead Stygian Doll damage: 61-98 (79.5 avg) hit points: 2901-6249 (4575 avg)
=> hit points / damage: 57.55

Demon Steed damage: 134-211 (172.5 avg) hit points: 16693-25964 (21328.5 avg)
=> hit points / damage: 123.64

Hell Cat damage: 40-72 (56 avg) hit points: 2471-5492 (3981.5 avg)
=> hit points / damage: 71.10

Moon Lord damage: 74-139 (106.5 avg) hit points: 10507-17511 (14009 avg)
=> hit points / damage: 131.54

Grotesque Wyrm damage: 38-67 (52.5 avg) hit points: 2318-4327 (3322.5 avg)
=> hit points / damage: 63.29

Grotesque damage: 76-124 (100 avg) hit points: 9274-15455 (12364.5 avg)
=> hit points / damage: 123.65

I think we're getting it by now. Enemies that have a hit points / damage ratio that is noticeably < 100 are ideal victims for Iron Maiden, while it gets long-winded against such with a ratio > 100.
Of course, we're speaking of melee attackers here.

Also there's the 'occasional' (rather frequent) situation, when I don't agree with above statement:
Whenever the monsters are ranged and/or magical attackers, IM has to be changed to amplify damage asap.

The number of enemies plays a role, too: When my dear golem and my hireling are being swarmed by a dozen fast attacking enemies, I always pull out IM. Then I support them by hitting one enemy with Bone Spirit, and when he's dead, I cast Corpse Explosion to quickly deal with the remaining monsters that have 50%- 75% of their hit points left. Of course my golem needs an occasional recast, and my merc needs potions during the process.
When we encounter only a few pitiful foes, however, I pull out AD. My merc deals a good portion of damage as every good merc should, and that takes care of most enemies quite quickly. If he doesn't want to take on our enemies, and has gotten stuck somewhere (happens quite often :angry:), I have to rely on my golem and my bone spirit to kill the enemies off (combined with some skeleton mages for cannon fodder. And no, I don't have the runes for an Enigma). That's the time when Lower Resist shines. I cast it and suddenly my golem can deal damage! It's not as much as my hireling, but if he doesn't want to.... Pfft.
Generally, physical immune enemies are dealt with AD. That's enough to let my merc take care of.

One more thing: The perfect necro (without decrepify) deals with groups of fast attackers in the following way in my opinion:

o stand back and let your golem, hireling, skeletons or what else is available tank
o cast Iron Maiden on the group of fast attackers
o help kill the first enemy
o switch to Amplify Damage and curse the group (it helps the CE)
o start to cast Corpse Explosion to quickly get a chain reaction
o heal / recast minions, and collect items :w00t:

So a quick guide when to use which skill would be:

AD:
o single monsters
o small groups of fast monsters (2-3)
o small to quite large groups of slow monsters (2-8)
o shortly before CE
o ranged and or magic enemies
o physical immune monsters

IM:
o medium to large groups of fast monsters (4+)
o rather large groups of slow monsters (9+)
o at first sight of the group of foes
o when the merc is somehow unable to really hit the enemy (such as duriel sometimes:unsure:)

Each of them has it's eligibility.

Sadly my necro is having major problems in hell difficulty. Maybe the merc needs a new armor, but times are tough for my necro, and leveling is slow. I knew that, of course, when I chose fire golem as one of my main spells, but it's nevertheless a bit - annoying. I'd never give up on my little hot-headed friend, though;).

Greetings, Fragbait