You cannot stack degrees of concealment, as [MENTION=16285]irdeggman[/MENTION] correctly pointed out.
The FAQ only says this:
D&D 3.5 main FAQ said:
Would a sneak attack work on a creature affected by the blink spell?
Yes. Blink doesn’t provide concealment, so sneak attack functions normally against a target affected by that spell (though such attacks would have a 50% miss chance, as normal for the spell).
From this I'd derived that, as long as they're not based on concealment, different kinds of miss chance would apply separately (and accordingly, rolled separately). Blink, Displacement, Entropic Shield (for ranged attacks) and Incorporeality are the ones I can think of, and would all apply at the same time, separately from each other, creating multiple opportunities to fail a roll.
However, the Rules Compendium has a drastic stance on the matter, to the point of being retarded:
RulesCompendium said:
Multiple concealment conditions don't stack. If a creature receives miss chances from multiple sources, such as from being incorporeal and having concealment, only the highest miss chance applies.
The reason this is retarded is that missing a Spectre due to incorporeality is totally different from not being able to see it perfectly. It is just slightly out of phase with the material world, so it can happen that you simply encounter no resistance with your +1 Longsword, and it may
also be that,
at the same time, you can't see the Spectre very well, so you're swinging wildly and simply miss. A Ghost Touch weapon negates the incorporeality problem, but not the concealment problem. An analogous argument can be made for Blink, Displacement, Entropic Shield etc.
So
I'd rule that you
can stack the miss chance from concealment with other chances of missing outright - as long as these are not concealment-derived. However, the official rules differ on this.
For example, in my game Blur, Mirror Image, Blink, and Entropic Shield would all work, separately, against one ranged attack. The attacker would have to roll over 20% in order to not be fooled by the concealment afforded by Blur. He would have to roll again in order not to have his projectile deflected by Entropic Shield. There's another 50% chance that you happen to be blinking out of phase at the moment the projectile would strike, rolled separately again
(this chance becomes 20% if the attacker has See Invisible running, implying that Blink's effect relies partly on concealment, but we'll leave that bit out since it complicates matters even further). Finally, the attacker must roll whether he aimed at the correct 'you', due to Mirror Image.
You can easily stack up huge 'effective miss chances' this way.
But by the book, effects that outright grant a miss chance don't stack. Probably to save us a lot of die rolls.
Note that even after the Rules Compendium, Mirror Image goes nicely with your Displacement/Blur/Invisibility/Blink, since it only creates a (positive) chance of hitting an image instead of the caster, not a (negative) chance to miss the caster outright. The FAQ's ruling on Mirror Image still stands:
D&D 3.5 main FAQ said:
Will fog or foliage produce a miss chance for a foe that aims an attack at an image? What about magical concealment, such as a blur or displacement
spell?
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.
