This comment and the other comments about DR 15/can't be beaten being things PCs can deal with seem to me to substantially misunderstand the way hardness and unbeatable DR effect combats.
For instance, I haven't seen the barbed devil's stats but assuming that it also has DR 15/Can't be beat by a Balor, the effect is not a close battle that's likely to be long and drawn out. Assume that the devil has 100 hit points and 2 claw attacks for 1d8+11 damage (average 15) and that the Balor does Pit fiend damage (none of these assumptions are likely to be accurate representations of the game statistics but they will serve to accurately analyze the effect of unbeatable DR).
The Barbed devil wil likely deal no damage to the Balor 50% of the time and 1-4 points of damage the rest of the time. It works out to be an average of 1.25 points of damage per hit. Assuming a 50% hit ratio, that's some 200+ rounds for it to defeat a Balor.
The renamed Pit Fiend version of the Balor, OTOH, will deal upwards of 22 points of damage/round (more than that really--that's just taking the average damage and subtracting 15 from it which doesn't accurately calculate average damage as demonstrated in the above example where average damage-15=0 but average damage really equalled 1.25; I'm assuming that the difference between the average-15 figure and the actual figure will account for my failure to calculate the chance of hitting). At that rate, the barbed devil will only last 5 rounds.
What this reveals is that unbeatable DR on both sides emphasizes the difference between damage outputs. The Balor may deal significantly less than double the Barbed Devil's average damage per round without DR but deals over ten times the amount of average damage/round after DR is taken into account.
What happens when one side has DR and the other doesn't (note that the Titan cleverly has an adamantium warhammer--thereby negating any advantage that a PC might otherwise gain from Stoneskin) is the subject of the next analysis.
Ftr 20 Str 30, Greater Weapon Specialization, +5 Brilliant Energy Greatsword or Longsword. Attacks at +37/+32/+27/+22 ignoring armor bonusses. Deals 2d6+24 damage (greatsword) or 1d8+19 damage (longsword) for an average of 31 or 23.5 per hit.
Assuming that a CR 20-21 villain has an AC of 40 (ignoring armor, this is the range that the Titan and the Pit Fiend appear to be in) and 300 hit points, the greatsword works out to an average damage of 27.9+20.15+12.4+4.65 or 65.1 points of damage per round (excluding crits) before DR. At that rate, the villain will survive 5 rounds. After DR, that is 14.4+10.4+6.4+2.4 or 33.6 points of damage per round. The DR extends the villain's life to 9 rounds.
The longsword wielder, OTOH, deals 49.35 points of damage per round before and 17.85 points of damage per round after DR. The DR extends the villain's life from 6 rounds to 17 rounds.
Assuming that the opponent attacks for 4d6+27 points of damage at +37/+32/+27/+22 and the fighter's AC is 39 or 41 (+5 fullplate, +5 amulet, +5 ring, +1 dex, +5 large shield or +3 animated large shield), the opponent will deal 77.9 (AC 41) or 94.3 points of damage per round (excluding crits and quickened Spell like Abilities--a feature of both the Titan and the Pit Fiend--and the effect of unseen feats like Awesome Blow). Assuming that the fighter is quite tough (240 hit points), he will still be dead by round 3 or 4 without healing. If the fighter uses Expertise and other feats to push his AC up to 46, he'll still take an average of 45.1 points of damage per round--potentially enabling him to survive to round 6 without healing (although with decreased damage dealing capacity)
In this case, the fighter's ability to defeat the creature's DR is what makes the difference between him being a significant threat who could potentially cause serious damage to the creature to either a minor threat who can easily be killed before dealing half the creature's hit points (greatsword) or an insignificant threat who the creature can swat before he deals even 1/4 of the creature's hit points in damage.
Someone with the inclination can run the math including power attack if they want but I expect that if it does anything, it will skew the scales even further towards the creature and the greatsword fighter. However, I think this analysis makes it clear that the ability to penetrate DR--even a "mere" DR 15--is not optional--even for high level fighters.
coyote6 said:
Even if fiendish DRs are only bypassed by good/holy weapons, the big bad fiends (who one would expect to fight the opposing big bad fiends with hefty DR) posted so far have had fairly large damage boosts, IIRC. Average claw damage from the new barbed devil is 15 pts; that means that half their hits will pierce the DR of a balor (assuming balor DR is 15, like the pit fiend's) -- and the barbed devil is significantly wimpier than a balor. The pit fiend's average damage amounts are 23 (x2), 14 (x2), 21, and 16; constrict average damage is 37 (!!).
Basically, a fight between equally matched opposing fiends will simply be a long, drawn out affair. Which is fine with me; it helps explain how their enmity lasts for eons (nobody can quite get an overwhelming advantage).
