The DC to identify the creature and gain knowledge on its special powers and vulnerabilities is based on its HD (and therefore, in theory, its rarity). The more you exceeded this DC, the more pieces of information you know about the creature. The DM will calculate this DC for you and will also chose which pieces of information you know. This give the DM control over how much advantage you gain from this skill (but a good one will use it fairly).
Every monster and/or race in D&D has a Type, and this type determines which skill you need to identify that creature. These are listed below:
- Arcana - constructs, dragons, magical beasts
- Dungeoneering - aberrations, oozes
- Local - humanoids
- Nature - animals, fey, giants, monstrous humanoids, plants, vermin
- Religion - undead
- The planes - elementals, outsiders
As you can see, some skills can identify more types than others, but if the adventures are well balanced, there will be a good mix of creature types so that no one person can do all the identifying.
That concludes this first Skill Focus. I hope you find it useful, and that it answers some common player questions. Look out for the next instalment.