Sir Aubergine wrote:[quote="ColorBlindNinja61"
Also another interesting question for those wiser than I (i.e. everyone). Castlevania has a pokemon thing going on where monsters are usually weak to a couple of elements and resist certain elements (damage from weapons is included in the rock-paper-scissors).
I generally think having vulnerabilities is a good thing. Implementation matters.
If a low-level enemy can ONLY be killed by the right material, that creates a very different experience than if they're EXTRA VULNERABLE. Sometimes nobody cares about the extra vulnerable - if I have a sword that does +2d6 fire damage, and I have a jade sword that does +2d6 against evil demons, unless the demon is resistant to fire it doesn't matter which one I use.
If you have any enemies that regenerate/heal it could be worthwhile to say they cannot do that in any round they've taken damage from a vulnerable substance - that'll give a clue to PCs that they have a certain vulnerability.
Ultimately, it should be another tactical decision - knowing you can get extra damage is good; needing to get the extra damage to have any chance of success is usually bad.
3.x tries to do this with DR that's overcome by certain materials. The places where it tends to fall flat are when you're stacking multiple different types of DR. Flipping DR to the the other side of the equation (ie, bludgeoning does +10 damage to skeletons) might work better.