The basic Rogue poisons last for 30 minutes and stack in piles of 20 in your inventory. They do not stack with other weapon effects like sharpening stones, Windfury totem, or oils made from Alchemy or Enchanting though. And no, Rogues shouldn't even be considering using any Enchanting oils in the first place, but after some of the shenanigans I've seen lately in PUGs, I wanted to be clear on that. (By way of example, I had the honor of running with a Rogue who stood in the back and shot everything with his bow as opposed to closing to melee.)
I generally tend to keep what I call "meat in mind" -- if the mob you are facing would be made of meat if they were real, then you're probably going to be able to poison it. If it's something else -- say, a rock elemental -- you're probably better off hoping for a Windfury proc, or reaching for a sharpening stone. Trial and error will teach you which will and won't work, and so long as you're ready and able to switch to another option before the next pull, most groups won't mind your experimenting. (Don't hold your group up playing swap the poison, though!)
A Rogue's bevy of poisons range the gamut from adding lots of sweet, sweet damage, to slowing your opponent as s/he runs in fear from you. That said, here are a few basic notes on what each poison does, levels, and some immediate notes that spring to my mind.
- Instant Poison - As the name implies, an instant-cast poison that does a certain amount of damage, depending on the rank. One of the first poisons in your repertoire, this is a solid favorite of many Rogues, and can work in the majority of situations. You get this starting at level 20, and gain ranks from there at 28, 36, 44, 52, 60, and the last (currently) at level 68. I generally carry two stacks of this around, because I tear through it in nothing flat.
- Crippling Poison - This is the other basic poison a new Rogue will get. It adds a slowing snare type effect on a mob for 12 seconds. The first rank at level 20 slows them 50% when it lands (30% chance, 40% with the poison talent) and will slow them 70% at level 50 when you get your second and final rank. This is lovely when you're heading into a situation where you're going to get a lot of social mobs that like to run and get friends. Also fairly nifty in PvP, if only to make folks waste reagents/mana/time getting rid of it. :)
- Mind-Numbing Poison - This does to casters what lack of sleep and too much caffeine does to any gamer who has ever gotten a game at a midnight release party -- brainfry! In essence, it causes casters' spell-cast time to increase by 40% at 24, 50% at 38, and 60% at 52 over 10 seconds. Most of the time this will not work on bosses (Pathaleon in Mechanar being an exception, for example) but this can be quite handy in PvP, or in cases where you're going to have to mow through a bunch of nasty casters to get to your target.
- Deadly Poison - A wonderful DOT that stacks up to 5 times, which you'll pick up starting at level 30. Now, when you pick up Shiv at level 70 and combine it with Envenom (levels 62 and 69) Deadly on your off-hand weapon can create some sexy numbers. It's also great for annoying other Rogues in PvP because stealth/vanish is worthless when you're DOTted up. However I must stress one thing about Deadly that I've seen time and time again... Unless you're 100% sure that your blades/maces/fists of fury aren't going to go flying and smack the wrong thing, please don't use this poison in groups where you're going to be dealing with a lot of crowd control -- especially in close quarters. All it takes is one auto-attack switch to the CCd target, an unintentional proc, and suddenly you've got an angry mob and an angry CCer telling you to tank it since you "spanked it." (Bonus Suck Points if that angry CCer also happens to be your healer.)
- Wound Poison - This reduces the healing that can be done to a target as well as being a marginal damage poison that you get at level 32. Sure, it doesn't sound like much, but when used in PvP, this can be truly unpleasant. Pile it up on the flag carrier and watch him fall over despite your opponent's best efforts! When you add in that it stacks up to 5 times, it can get downright nasty.
- Anesthetic Poison - Available at level 68, this is by and far my favorite poison for instancing, hands down. It's also the "newest" poison for Rogues, as it was introduced with Burning Crusade. While it doesn't do the highest damage, the fact that it causes no additional threat makes it a wonderful choice for raiding and instancing. Sure, it's only a 20% chance (30% with talents) to land, but with Shiv, you can certainly drive your poisoned point home without fear of the same threat you'd see off-handing Deadly.
In short, get to know your poisons, and it will pay off in higher numbers, better instances, and happier CCers. All it takes is a bit of time, a bit of research, and a bunch of dead "test" mobs. But hey, you were going to kill them anyway
... How about you? Are there any combinations of poisons you swear by, or particular mobs you've developed good one-two poison strategies for? For the rest of you, any poisons you love to hate?