Effectiveness of -DMG as Mitigation?

Soething I've wondered about for a long time.

There are a number of powers that reduce enemy damage, notably Dark Miasma's Darkest Night toggle and Kinetic Melee's extra effect, among others (even Shield Defense gets a little of it in Against All Odds). It does not appear to be an enhanceable property.

• Does it stack from different sources?
  
• How effective is this mechanic at increasing character survival?
  
• Does it reduce the final damage you would have taken by the stated percentage? I.e., does -10% damage reduce a 100-point hit to a 90-point hit, or is it factored in somewhere in the formula, like damage enhancement in a player's power, meaning it does not reduce final damage by the full 10%? (Not sure I'm expressing that intelligibly, sorry.)
  
• Is it reduced by AV resistance (which is 85%, iirc)?
  
• Assuming it's at least somewhat useful, what powerset combinations would give the most -damage? I am inclined to think it would synergize with damage resistance pretty well, so maybe pairing -dmg with high resistance would be best? Perhaps Kinetic Melee / Electric Armor?

1. Yes, like all buffs and debuffs
2. Umm, somewhat. It's not enhanceable, which limits it's effectiveness
3. Against an even-con minion, it will reduce damage by the stated percentage. The damage enhancement issue faced by players is due to the assumption that most people run with ~95% damage bonus due to enhancements in their attack powers. -Dmg is basically a negative Damage bonus, and is subtracted from the total damage bonus on a character. I.E it'll do next to nothing to someone who is Fulcrum Shifted.
4. Yes. It is subject to the purple patch as well, so it is resisted a bit by Bosses, and significantly as one moves up the con ladder.
5. Not sure, I imagine stacking the -dmg from Kinetic Melee would work well with -dmg from darkest night and either Shield or Ice Armour.

-DMG is effective, it's just not quite as effective as straight-up Resistance. But it can work. Like NoiseBlind said, it does scale with enemy level to you, so the higher the enemy, the less -DMG you will inflict.

But if you can stack it, it works as straight damage reduction, and will stack from different powers. An Ice/Kin/Soul Tanker can make excellent use of the -DMG mechanic to become very survivable.

I tend to think of -dam like a resistance shield and -tohit as a defense shield.

Darkest Night is 37.5 -damage (unenhanceable) and 18.75 -tohit (enhanceable). That power, by itself, is better than most melee armor sets until about level 25 or so when they have enough slots and enhancements in those slots. And it works against all positions and all damage types!

I want clarify that it is NOT subjected to the 85%ish AV resistances (which was already done above by Trick).

I just took my Kin def out to see what the effects of -dmg was, in actuality.

Against an even con (lvl 51) lieutenant, it was a 25% debuff that resulted in a 25% damage reduction.

Against an even con boss, a 25% debuff resulted in a 25%% damage reduction, boss had no resists. Against another boss with resists the -dmg was = (1-resist) * .25

Against an even con AV (Diabolique), a 25% debuff resulted in a 12.5% damage reduction 50% resists across the board. So there is NO AV resistance.

So, to the OP's 5 questions.

1) answered upthread
2) Pretty darn effective
3) Right, subjected to level adjustments and damage resists.
4) Answer in this post above
5) I wouldn't say -dmg particulary synergizes with resistance more than defense. If anything, it mainly "synergizes" with itself.

Damage can be a confusing mechanic because of how it's handled by the game. Let's take a brief moment to review the fundamentals of the powers system.

All entities in the game (in this case, we're talking about player and non-player characters) have several values associated with them. These values are called "attributes," and there's a significant number of them. Every distinct component of an entity fits into an attribute: Endurance, Defense types, Influence, Mez types, Regeneration, etc. If there's a number associated with an entity, there's an attribute to hold that number.

Attributes themselves have a number of modification values associated with them, which the devs gave the non-descriptive name of "aspects." These include the direct values, resistances and strengths of the attributes, to name a few. The "direct value" includes anything with a quantity, such as Endurance, XP, Influence and status effects. Resistance and strength, applied to an attribute, affects all modifications of any aspects of that attribute on the target. More on that in a bit.

Damage types are special case attributes in that the "direct value" for all of them map to the same thing: Hit Points. Subtracting 5 from Smashing Damage is exactly the same as subtracting 5 from Fire Damage. That is, they both result in a loss of 5 HP by the target. However, each damage type attribute still retains its strength and resistance aspects, meaning it's possible to resist, as an example, 50% Smashing Damage while resisting 0% Fire Damage.

As I mentioned a couple paragraphs back, resistance and strength on attributes apply to all attempted adjustments to any aspects of those attributes. In the case of Smashing Damage, for instance, 50% resistance will halve the amount of HP depleted, as well as halve all debuffs to resistance and/or strength for that damage type. For this reason, almost all "buff" effects are set to be irresistible: they will apply at their full strength regardless of the target's resistances. However, "debuffs" can be resisted.

In the case of -Damage, it's actually a compound effect. Reducing the damage of the target is actually an adjustment of the strength aspects for all 8 damage type attributes of the entity. The 8, for reference, are Smashing, Lethal, Fire, Cold, Energy, Negative Energy, Psionic and Toxic. Most enemies have some form of resistance to some of those, meaning the portion of the -Damage effects that attempt to adjust them will be resisted accordingly.

In the same way, -Resistance attempts to adjust the resistance aspects for all 8 damage type attributes, and likewise can be resisted.

To answer an earlier question: yes, applying -Resistance first WILL increase the effectiveness of a subsequent -Damage.

Unlike tohit built on top of defence, where the mob will still have 5% chance to hit, -damage can be built on top of resistances to effectively bring a toon beyond the resistance cap. Say a sonic/dp(chem rounds) defender paired with a resistance capped stone tank... The effective resistance for the tank could be brought to up 99% resistance.

Against how many mobs and how consistantly though? I am unsure. I never did get around to building the toon. If I remember correctly though, it was theoretically possible for me to get upwards of 50% resistance on top of softcaped defence. Will have to take another look at it, especially considering the resistance bonus changes. Also, considering how hard it is to kill a resistance capped tank, beyond ***** and giggles there really is no reason to do it.

The nice thing about sonic is that it does -resistance as well, so your -dmg is even more effective.

Yes, it does stack, if you have multiple sources of it. Single powers may or may not stack with themselves, check the detailed power info to be sure. It stacks linearly, so a -20% and a -30% debuff will result in a final damage reduction of 50%. As mentioned above, it also "stacks" with +DMG (technically it's the same thing, just negative). So if the target has damage buffs, it'll counteract those before it starts reducing damage. (+100% buff from Build Up - 50% debuff = +50% relative to base damage).

What I didn't see answered or asked is what the caps are. The low end of the cap is 10% strength in almost all cases*. That means you can stack up to -90% damage (de)buff, and the target will only do 10% of the damage they normally would. **

* The cap is 10% for all player ATs and nearly all NPCs. The Rularuu AV in the Cathedral of Pain Trial has a 50% cap below which it cannot be debuffed.

** Note that some powers, like Tyrant's Flow Lightning, ignore debuffs (and that one does a fixed percentage of the target's max health anyway). These are fairly rare, but also mean they don't benefit from buffs either, like the +DMG he gets from absorbing Olympian Guards.

I have minimal experience with -DMG powers. The only one that employs such a tactic is my kin/elec armor stalker. I have him equipped with tier 4 paralytic radial, and also Void radial final judgement and duplicity.

So far, the -damage powers have been largely ineffective at increasing his durability by anything noticeable. Most regular enemies don't survive long enough for the -damage powers to stack, and will also expend all of their attacks before it ramps up to meaningful amounts. While fighting AVs, the -damage peaks and sustains a total of around -30%, making it so enemies that would steamroll him still do steamroll him. There is a noticeable increase in survival after using void judgement, but otherwise it will not keep my stalker alive in a situation that he would not have previously survived if he didn't have the -damage abilities.

Dark Miasma has Tar Patch which is -30% Resistance. And that can be stacked since it's from the pseudopet. So, a very high recharge Miasmist can put out -60% Resistance for half the time and -30% the other half.

Also, Fluffy has Darkest Night, too. So, if you can get the target isolated, Fluffy will throw another -30% DAM on top your your -30% DAM.

(And not to mention getting over -80% ToHit, up to -120% with slotting.)

Is it effective? Anecdote time:

Remember when the STF used to be hard? And the Master of the STF even harder because of Ghost Widow and her 100 Mag Hold that would auto-kill even the hardiest Tanker? Well I don't. Because of all the -DAM my D3 had. I'd see squishies survive GW's hold. I didn't know what people were talking about with all that auto-kill talk. The same for Boobcat's ridiculous 3k damage. It's never that high and instganking people when my D3 gets all his debuffs running.

Getting a better understanding of the relationship of -dmg and -res has given me a deeper appreciation of my Kin/Sonic Defender. That's saying something because I've always thought of him as one of my top 2-3 team contributors.

Yesterday when compiling the results I got upthread, I was just spamming Siphon Power and Fulcrum Shift and debuffing Diabolique (with resists of 50% to most all damage but Psi) and seeing the -dmg debuff range from -50 to -75, typically at -62.5 (final numbers after all adjustments).

Just now I went back and worked in my Sonic attacks between Siphon Powers and FSs and was able to get to -90 (cap) a good chunk of time. Mostly Diabolique's damage was -80ish.

I created the Kin/Sonic with the intent of abusing the damage cap with Kin buffs and Sonic debuffs. I had no idea the synergy worked the other way too, in debuffing enemy damage in this manner. /em Rafalca_Fancyprance

I remember I was surprised how effective a Kinetics Defender was against AVs. Much of this was due to the -50% damage you can put out straight away with Fulcrum Shift and Siphon Power.
Of course, this trick didn't work against Infernal, who has massive Fire resistance and does Fire damage.

The augmentative relationship between -Resistance and -Damage is the basis of two of my characters: a TA/Sonic Defender and a DP/Poison Corruptor. The former stacks -resistance from Sonic with more -resistance and -damage from TA while the latter stacks -damage and -resistance from DP with more of each coming from Poison. It's very effective and nice to play with a non cookie cutter build.