Concealment is a condition in which the target with concealment is more difficult to hit than they normally would be. Having concealment grants a flat miss chance for attacks made against you. We all know this since it’s a core rules mechanic.
As we all also know, having concealment is great. It’s better than cover in most situations because even if someone that’s trying to hit you has a huge base attack bonus, they still have a blanket miss chance that applies regardless of their modified roll.
Let’s look at a fairly easy way to get a hefty amount of concealment.
Spells
As with most things D&D, one of the easiest ways of accomplishing a certain objective is with magic. In the realm of obtaining concealment, two spells jump to mind: Blur and Displacement. Both work in slightly different ways but give similar effects. Another option that works in a very different way is Mirror Image.
Let’s look at how blur & displacement work with each other and then how mirror image comes into the mix afterwards.
Blur + Displacement
We all know that effects “do not stack if they have the same type or come from the same source”, but when we look at blur and displacement, this doesn’t appear to be the case. The bonus of concealment isn’t a typed bonus and the source is obviously different. Further, the effects as written in the spell description are widely different from each other.
Blur:
The subject’s outline appears blurred, shifting and wavering. This distortion grants the subject concealment (20% miss chance).
Displacement:
The subject of this spell appears to be about 2 feet away from its true location. The creature benefits from a 50% miss chance as if it had total concealment. However, unlike actual total concealment, displacement does not prevent enemies from targeting the creature normally.
In the case of blur, your form is distorted, which gives you concealment. However, in the case of displacement, you’re actually in a different spot from where you’re perceived to be. These effects are clearly different.
If they’re different, then they can stack – but what’s the nature of their stacking?
I think a flat 70% miss chance is absurd. I can see someone making an argument for it given this line in the concealment description under “Varying Degrees of Concealment”:
Certain situations may provide more or less than typical concealment, and modify the miss chance accordingly.
(this is copied right from the System Reference Document, which either makes it a typo or poorly worded sentence. We know what they’re trying to say though.)
What makes more sense is to have two miss chances. The first would likely be for displacement since the person isn’t even where they’re believed to be. This would then be followed up by the miss chance for blur, since their form is more difficult to hit due to the effect.
That seems to work well with the rules, is consistent with the spell descriptions and isn’t as over-powered as just adding the miss chances together.
Blur + Displacement + Mirror Image
Mirror Image is a great spell. It’s not super powerful because your mirrors have a relatively low AC (10 + your size mod + your Dex mod). At the very least, however, it can offer you a round or more of immunity to melee and ranged attacks if you’re lucky.
The question is, of course, “do the effects of blur or displacement apply to my images”? The answer, fortunately, can be found by looking at the trusty FAQ. To save you the time of reading the whole thing, I’ll paste the part that’s important:
If the user has concealment from her surroundings, the images have the same concealment. The images also look just like the caster, and they share purely visual effects such as the blur or displacement spell. If the mirror image user is also using either of these effects, an attack aimed at an image has the same miss chance an attack aimed at the caster has.
Remember, this is right from Wizards.
Personally, if there wasn’t a ruling on the FAQ, I would say that an image receives the 20% concealment from blur, but does not receive the 50% concealment from displacement.
If you look at the displacement text, it doesn’t say that you “gain concealment”. You gain a miss chance “as if you had concealment”. The difference is subtle, but there. And since the images of you are moving about, this seems to negate the displacement effect. But since it’s an exact image of you, it inherits the visual effects (and thus benefits) of blur.
In a case in which you would be hit (opposed to one of your mirror images) then you could benefit from both blur and displacement. Your opponent chose the correct “you”, but you weren’t where they thought you’d be due to displacement.
The Cost
Getting all this to work requires 3 rounds. Without some way to quicken one of these spells, that’s a pretty significant amount of time during combat. Luckily blur and mirror image last a minute per level.
I would personally lead off with mirror image, which gives you a 50-80% miss chance right off the bat – which certainly competes with displacement in the first round.
Round two is a tough call – do you go for displacement, which is a higher bonus or do you go with blur, which has a much longer duration? If you were set on using all three, I’d go with blur. If you weren’t sure what you’d be doing the next round, then displacement may be better to fire off in case you do something else. It’d be better to have the more-powerful effect in place even if it lasts a shorter period of time.
Is It Even Worth It?
If you’re a 5th level PC going into a hefty battle, then I’d say it certainly is. Most wizardly types at 5th level don’t have hit points to spare even on little hits. The last thing you need is an archer readying an action to knock you out when you cast a spell.
Short of blindsight and true seeing, there’s little that negates miss chances – which is why they’re so powerful. Cover is great in that it gives you an AC bonus, but a well-timed truestrike puts that to bed real quick. Even with a +20 to hit, if you don’t make your miss chance roll against someone with concealment, you miss. It’s that simple.