No good options on this poll, unfortunately.
They should do three things with Damage Reduction, IMO:
1) With the exception of vampires and werewolves, they should remove DR entirely from all categories of monsters. If a monster is supposed to be extremely tough to kill, there's already a better mechanic for that - lots of hit points.
2) For unique, named monsters they should consider keeping DR (or, better, Vulnerability), but instead of having it keyed to one of five special materials (silver, cold iron, adamantine, magic, alignment) it should be tied to a unique named item/ritual/whatever. (Perhaps that demon lord is vulnerable to the sword of the paladin who beat him last time.)
Doing this eliminates the 'golf bag' mentality. In 3e/4e, players quickly reach a point where almost every encounter is against a creature with
some resistance, but that that resistance can be bypassed with one of five materials. Under those circumstances,
of course they're going to want a 'golf bag' of weapons to deal with it!
By restricting DR to unique, named individuals and to unique, named countermeasures you make it much more memorable - both the bad guy and the magic item have built-in flavour. Additionally, there ceases to be any reason for the 'golf bag', since the weapon that worked this time won't work next time. And, finally, it gives the PCs an interesting choice - do they quest to go get the unique magic item, or do they take on the monster without it at greater risk?
There is an exception to this:
3) Vampires and werewolves are special cases, because these are classic monsters with well-known and iconic vulnerabilities. (I think they're the
only such iconic cases, but I may have forgotten some?) Here, I recommend taking a look at two recent films for inspiration:
In "Dog Soldiers", the werewolves are really tough, but they
can be taken down using normal weapons. That is, they have lots of hit points. However, the soldiers also have a small number of one-shot silver weapons that are extremely effective. I would recommend modelling this by eliminating the concept of 'silvered' weapons entirely, and instead having
silver weapons that, if used, quickly become useless (like magic ammunition in 3e). Oh, and give the werewolves a very significant Vulnerability to such weapons, of course!
In "From Dusk Till Dawn", the vampires are also extremely resistant to normal weapons. However, after that initial encounter the heroes then proceed to construct themselves a number of better weapons - they whittle stakes, bless holy water, improvise holy symbols, and the like. Having done this, they could effectively ignore the resistance for the rest of the film. In game terms, that is of course easily modelled - an easy-to-use ritual that can be cast during a short rest. That way, you get the initial 'shock' encounter of vampires that can't be killed, followed by a rest, and then on with the fun vampire-killing antics! (Plus, it means that groups don't have to carry lots of vampire-killing gear for that once-in-a-campaign adventure when they suddenly need it.)
Incidentally, Vulnerabilities are generally more satisfying that Damage Reduction, and simply giving a creature lots of hit points seems to be a better way of making a monster really tough (in general).
I think DR/Vulnerabilities can be a fun mechanic. But they should use it very sparingly, and make it count.
