Suggestion: A Monster Vulnerable to Bone

[Arcanemuses]

Here's the idea. Make a monster with a high DR, and make it weak against bone. Basically DR 10/bone. In this case, bone counts as weapons fashioned from bone, strikes/slams from bony appendages, and bite attacks (teeth). That'd be cool.

[Ascalaphus]

Sure. Or DR/obsidian, DR/diamond or even just DR/wood.

There might be a niche for DR/organic; where organic is bone, leather, wood etc. Something for druids who take the "no metal armor" to its far extreme.

[Petty Alchemy]

Sure, though bone is a strange choice. In After Sundown the special materials are as follows:

After Sundown wrote:

Wood

In many songs and stories, only special wood counts against the forces of darkness. Maybe it is oak, or banyan or sacred ash. But seriously it doesn't even matter. Wood represents life even when it is dead, dry, and laminated. It is effective against Animates, Vampires, Zombies, and Ghosts.

Iron
Seriously, Iron. Like the stuff that your steel knives are already made out of. It's a symbol of modernity and industrialization and stuff and it classically drives away the old cthonic stuff. It is effective against Leviathan, Transhumans, Evil Plants, and Fey.

Silver
Shiny and inconstant like the moon, silver is hard enough to kill a man and easy enough to cast that you can do it before the invention of bronze. Silver is clearly magical, and is lethal to creatures as ephemeral and primal as it is. It is effective against Witches, Lycanthropes, Giant Animals, and Demons.

Bone could perhaps be as Wood, organic like Ascalaphus said.

[Bardarok]

I'm with Ascalaphus on this one use whatever special material to bypass DR that you like.

As a DM monsters with interesting DR material requirements make monsters more interesting. As long as there is an opportunity for the PC's to learn of the creatures weakness of course if not then it just seems cheap.

[Ascalaphus]

You might want to think a bit about the interaction with magical +X weapons though.

If you include lots of different DR, at some point the warriors will just get a +5 weapon and be done with it.

You could suspend that rule because it hurts your flavor, but then you should think about what that'll do to caster vs. martial balance (such as it is). If martials need a golf bag of weapons, and have to spread their money between enchanting lots of different weapons, casters should have some difficulties too.

I suppose one way of doing that is to make sure that every monster with odd DR also has one or more energy resistances and is immune to a couple of classes of SoS/SoD spells. Including some spells that normally bypass SR; otherwise the casters just switch to no-SR spells all the time.

Basically: if the martials can't use one trick all the time, casters shouldn't be able to either.