Of what value is reduction of damage from enemies? Conventional wisdom is that it's a normal difficulty: yes, higher difficulty: no, choice, but there's more than meets the eye. This article addresses the items, damage reduction, and stun elimination aspects. The abbreviation -dfe (minus damage from enemies) is used for items in the osmosis family.

This discussion focuses on 'key monsters' which are common and provide problems which -dfe can address. Looked at are illusion weavers (IW), lava maws and maelstroms (nasty fast attackers), azure drakes and BK's, and the toughest witches, Soul Burners.

With -6 dfe:

Monster	Norm	NM	Hell
IW	14	38	80
Maw	9	28	60
Mael	14	39	80
Azure	19	46	96
BK	24	58	120
Soul	12	34	72

Some monsters have a wide range of dmg, like 1-35 for soulies, which make the avg dmg calculation a bit complicated for large -dfe.

Let's define EHP as effective hit points, an equivalent number of hit points to compare to 100 hp with no -dfe.

Significant in low difficulties, but nothing major. Things get more interesting when you wear multiple -dfe items, as shown in this table.

(These assume you have resistance to magic for the soulie numbers.)

So how many HP is -dfe worth?

More extensive calculations along these lines were used for several typical cases, and some generalizations. Warrior with 500hp, DSC, HD+Gotter+DSC, and HD+Gotter+Carapace, Rogue with 250-300 hp wondering whether to use Stormshield or Holy Defender, a Rogue SNOB, and Sorcerer with 750 mana using Scavenger's Carapace.

(Of course, a dragon of 60 mana here is for MS defense only.)
Note also that if you have half the hp or mana given above (500/300/750 for W/R/S) its worth would also be half.

What about stun prevention?

Whether or not a character goes into hit recovery (stun) depends on whether the damage is greater than or equal to the character lvl (and less than the current number of hp). The following looked at min and max dmg for each monster, and saw when dfe took dmg below clvl.

What percents of hits become non-stuns due to -dfe?

clvl	DFE	Norm			NM			Hell
		IW	Maws	Drakes	IW	Maws	Drakes	IW	Maws	Drakes
20	-6	56	9	47	0	10	0	0	0	0
20	-12	56	9	87	0	38	0	0	0	0
20	-30	56	9	87	82	95	40	0	10	0
30	-6	0	0	20	0	33	0	0	0	0
30	-12	0	0	20	35	62	8	0	0	0
30	-30	0	0	20	94	71	80	0	34	0
40	-6	0	0	0	41	24	24	0	0	0
40	-12	0	0	0	76	24	48	0	14	0
40	-30	0	0	0	76	24	96	0	59	0
45	-6	0	0	0	41	0	28	0	12	0
45	-12	0	0	0	47	0	52	0	27	0
45	-30	0	0	0	47	0	80	15	70	0

Conclusions for Osmosis and Stunning:

Clvls below 24 facing Illusion Weavers on Norm benefit from dfe
Clvls in 20's on Norm benefit from some dfe
Clvls in 20's on NM would need massive dfe to benefit
Clvls in 30's on NM benefit nicely from around -12 dfe
Clvls in 40's on NM don't need more than a few dfe if any
Clvl 30 in Hell would need massive dfe even to benefit from maws
Clvl in 40's in H/H can use as much dfe as possible if want to avoid stun
Illusion weavers in Hell/Caves can only be stopped by max -dfe by ultra hilvl chars
Fast attackers in Hell/Hell can not stun 25% if clvl + (-dfe) is > 45

Unique Items providing -dfe:

-1dfe: Torn Flesh of Souls, Wisdom Wrap
-1 or -2dfe: Ring of Engagement
-2dfe: Gladiator's Bane, Holy Defender
-1 to -6 dfe: Wicked Axe
-4dfe: Gotterdamerung
-5dfe: The Protector
-6dfe: Demonspike Coat
-15dfe: Scavenger's Carapace, the King of dfe
+4 dfe: Stormshield
+1 to +6 dfe: Fool's Crest

Regular items:

Shield: up to Absorption -3, with Obsidian. Rare but possible.
Armor/Helm: Osmosis possible, with Godly a good suffix (Wirt).
Armor/Helm: Deflection, with Awesome and Obsidian available.
Health (-1), Protection (-2) can be on armor, helm, or shield.

Maximum dfe setups:

-30 dfe: Carapace, Osmosis helm, Protector, and 2 ROEs.
+24 dfe: Pain x6.

Practical setups:

Warrior, low to mid lvl (or mid lvl rogue)
DSC, Godly Crown Osmosis, Holy Defender for -14 dfe
Warrior, hi lvl
AFPDeflection, Godly Osmosis, Obs Sh Abs for -13 dfe
Warrior, SNOB
ScavCarap, Gotter, Holy Defender, 2 ROE for -25 dfe
Rogue, mid to hi lvl or SNOB
ScavCarap, Gotter, HD for -21 dfe
Sorcerer, Arty
ScavCarap, HD (DF,TC) for -17 dfe
Sorcerer, Battle
AFPDeflection, Obs Sh Abs for -7 dfe (-13 with Osmosis hat)

Slight twists on 'traditional' setups

High AC Warrior - Godly Osmosis vs Whale
Equal in NM, Whale in H/H, Osmo in Norm/Hell
High AC Warrior - AFPDefl+ObsAbs vs AFPLion+ObsTiger
Equal in NM, LionTiger better in H/H
High lvl Melee Rogue - SS vs HD
Difference is slight (Eagle) in H/H
  Equal to extra tiger in NM, but SS+10 str gets the nod if str is needed
        to wear full plate.
Arty Mage - SC+HD vs NLP+Brill
150 defense mana vs spell lvl and +30 mana, +20% resist, but also you get
        fast block and you're free from 25% of maw stuns around clvl 35-40
Arty Mage - Obs Absorption vs Jade Brill vs Holy Def
Jade Brill - up to 30% resist all, +30 mana
  Obs Absorp - up to 40% res all, and defense equivalent to 180/60/30 mana
        on Norm/NM/Hell hell
  Holy Def - fast block, 20% res fire, -2dfe worth 120/40/20

As it turns out conventional wisdom is fairly sound, but it's not black and white. Osmosis is roughly equivalent to other options in NM, a clear cut winner in normal diff, and playable although not as strong in Hell difficulty. Around clvl 45 it re-emerges as an anti-stun device against maws and maelstroms, or in massive doses, against illusion weavers.

I hope this is helpful. Feedback, corrections, game-based observations, are all welcome.  Send to Charisena@insightbb.com