Using Rot of Ages to enable sneak attacks

Question

This is more a question about 3.5e stealth mechanics than anything else.

The Rot of Ages spell grants all creatures concealment against the target. I would think this would enable a rogue to attempt sneak attacks against the target more easily, but I don't understand exactly how this would work - much of the stuff I read about concealment and sneak attack seems to assume that the rogue would have to leave concealment to be in position to make the attack.

Does the rogue still have to pass a hide check? Can he be hidden from only the one creature? Does he take any of the penalties for hiding while observed? Does it make a difference whether he has already made an attack or not?

Answer 1

Ok, let's start from the beginning.

When are you allowed to Sneak Attack your target?

From the SRD

The rogue’s attack deals extra damage any time her target would be denied a Dexterity bonus to AC (whether the target actually has a Dexterity bonus or not), or when the rogue flanks her target.

This means that if you can't flank your opponent, you will have to hide to deny his Dexterity bonus.

(I actually edited the following part, according to this question, linked by @HeyICanChan. Thanks!)

If you are observed, you cannot perform an Hide check unless you have the Hide in plain sight feat. In order to Hide, you should create a diversion first; You could use Bluff to achieve this result (as a Swift Action), but be aware that the generated Hide check is made at a -10 penalty because you have to move fast (as stated in d20SRD on "Hide"; This will be your Immediate Action). Getting out of sight and then sneak behind your opponent could be an easier solution.

Once you're not observed anymore, you need a place to hide: concealment grants you one; Without concealment you would have to cover to perform an Hide check, and in that case it could be pretty hard to perform a Sneak Attack because most of the times your cover is not right beside your opponent. Hiding is considered a part of your movement action, so it doesn't matter if you already attacked or not.

Rot of Ages makes an excellent work with this, because it gives you concealment against your opponent (only against the one that was targeted by the spell) while you are next to him, even if he passes the Fortitude save. Plus, the chance of him being sickened (-2 to almost everything) or even better, nauseated if you cast the spell again (can do nothing that requires attention, and can only do one move action per round. In this case you won't need to perform the Hide check) gives the Rogue the ability to Sneak Attack him even easier. This is absolutely perfect.