These were my initial thoughts on Damage Negation, as originally aired on the Hero Forums after the release of Hero System 6e.
I find myself intrigued by Damage Negation and have a few thoughts on it. First off, I like it in theory. It is a very elegant and direct mechanic. In practice, I have a few concerns, in no particular order.
It requires up-front modification of the dice rolled. This effectively rules out pre-rolled damage totals, a common GM trick to speed combat, being used against characters with DN.
It could also result in botched rolls if the roller gets antsy and throws the dice before the total is modified, or if DN is forgotten at first.
It makes AoE attacks even more complicated to resolve.
Some GMs go out of their way to keep combat descriptive and removed from mechanical labels, and DN flies directly in the face of that. As in the case of bad guys with DN, it forces the GM to communicate mechanical info directly to the players, such as, "Roll 6 fewer dice." In addition to the disclosure, this kind of conversation explicitly introduces meta-considerations and could lead to metagame decision-making on the part of the players ("I'll use my DN-negating attack next!").
The DN-hosing Reduced Negation adder introduces an instance of symmetrical rules elements, where X levels of an ability directly turn off X levels of another ability, as does Damage Negation itself. This has some interesting permutations mechanically, but really it seems to me that if such a model is in use, it should have been used more broadly as a core concept rather than as a tacked-on edge case. For instance, Armor Piercing (AP) and Penetrating and their corresponding hosers could have been reworked in this format on both sides (attack and defense).
Further, the commonality of attack Multipowers (MPs) and the cheapness of adding a slot suggests to me that most such characters will end up with a DN-hosing slot, particularly if the GM doesn't strongly enforce concept and make them really justify it.
I think that this idiom will make DN-based characters surprisingly brittle. Versus normal foes and environmental threats, DN-Man shrugs off damage; then MultipowerMan comes along, and DN-Man bounces the first shot but is creamed by the second after MultipowerMan switches slots.
At 2 points per level vs. 5 points per level, even a 60 AP attack can afford to cancel a sizable chunk of DN and still be effective, assuming DN-Man doesn't have decent amounts of traditional defenses. Three points per level of DN-hosing might have been a better price, but the underlying disparity is still there.
When you further consider that many DN-based characters probably split their points between Physical and Energy similar to the way most characters structure their traditional defenses, while an attacker only has to beat the DN across one vector, the disparity is even worse.
Personally, it seems to me that Reduced Negation should be more tied to special effects (SFX), particularly when priced at 2 points per level. However, as DN and Reduced Negation are both pure mechanics, doing this would likely prove difficult to define on a case-by-case basis.
For purposes of comparison, let us consider -6 Damage Classes Damage Negation vs. 30 normal defense (nDEF) vs. 20 resistant defense (rDEF).
-6 DN vs. 30 nDEF vs. 20 rDEF
The max roll of 6d6 normal damage is 36, while the average is 21. If Reduced Negation doesn't enter into the equation, Damage Negation is clearly better here even if you don't consider the knockback (KB) implications or the variety of other things DN can potentially protect against, such as a 6d6 AP or Penetrating attack.
The max roll of 9d6 is 54, while the average is 32. At 3d6 over DN, the range is 11 to 18. nDEF looks better here vs. average damage (taking 2 vs. 11), but DN still wins vs. max damage (taking 18 vs. 24).
The max roll of 12d6 is 72, while the average is 42; 6d6 over DN the range is 21 to 36. nDEF is still better vs. average, and DN is still better at max, but it's clear that the progression is degrading and eventually nDEF wins out vs. bigger attacks (though it's likely a Pyrrhic victory).
Switching over to killing damage, at 2d6k (6 DCs) DN still gets the win over rDEF due to its secondary benefits of effect cancellation.
At 3d6k (9 DCs), rDEF looks a whole lot better. The 1d6 Killing over the top of DN is going to really hurt, while the rDEF bounces it all.
At 4d6 (12 DCs) rDEF will bounce all but the highest rolls, while DN lets a lot of BODY damage get through even on average.
The STUN multiplier and any unresistant base PD/ED are the wildcards here, of course, but rDEF is generally better at stopping killing damage (as it should be).
It seems clear to me that DN is most effective when used as part of a hybrid defense strategy. A character combining DN with some other defense should be able to find some "sweet spots" where the risk of one is offset by another. A character with, say, 15 nPD, 10 rPD, and -3 DC DN for 45 points is probably doing better overall than a character with 30 rPD, 45 nPD, or -9 DC DN.
I won't be surprised to see characters with such hybrid defenses crop up. And to some extent, that's very normal; just as many Hero characters of past editions have freely mixed rPD and nPD as desired.
Overall, it seems pretty clear that Damage Negation is competitive with standard DEF-based defenses vs. vanilla damage. Its effect-stopping benefits are clear pros, but its vulnerability to a cheap hoser is a sharp con.
More specifically though, DN as Invulnerability kind of falls apart unless a character has very high levels of DN, as anything past the DN threshold gets through and really hurts. Similar to the effect of a vehicle's DEF, without some backup defense such a character will go from unhurt to broken quickly if they encounter something able to crest or ignore their DN.
The official published characters will give us a hint of what is expected, but just as in past editions, the local metagame of a given group dictates the prevalence of AP and Penetrating and Hardened defenses (I recall one GM's campaign where if you didn't have double-hardened defenses you would likely regret it due to his penchant for double AP or double Penetrating attacks, for instance). I think a similar effect will take place vis-à-vis Damage Negation vs. Reduced Negation.
Still and all, I like DN and think that it allows for some very interesting concepts to be realized.