Concealment

Concealment in DDO refers to Concealment Miss Chance

Concealment Miss Chance gives the subject of a successful attack a % chance that the attacker missed because of the concealment. If the attacker hits, the defender must make a miss chance percentile roll to avoid being struck. Multiple concealment bonuses of the same type do not stack, and currently almost every single one is considered the same type - enhancement.

Concealment from external sources, such as from a cloudkill also won't directly stack with concealment from buffs like blur. But since it is considered a 2nd source and different bonus type of concealment, it will force an additional percentile roll, so the monster may have to roll a d100, and get over 20, twice in a row to successfully attack you if you had both blur and he was subject to a cloudkill (and the monster otherwise was not immune to either, nor had True Seeing.

Enhancement bonuses to concealment are provided by:

 * Spell: Displacement. 50% enhancement bonus to concealment.
 * Spell: Shadow Walk. 50% enhancement bonus to concealment (lost if you interact/fight).
 * Spell: Blur. 20% enhancement bonus to concealment.
 * Spell: Fog Cloud. 20% AOE concealment. (Typed as enhancement though it seems like it shouldn't be)
 * Item effect: Smoke Screen. 20% enhancement bonus to concealment.
 * Item effect: Blurry. 20% enhancement bonus to concealment.
 * Item effect: Ghostly. Listed as a 10% bonus to concealment, but the effect blocks Blur spell and is confirmed to actually provide 20% enhancement bonus to concealment.
 * Item effect: Dusk. 10% enhancement bonus to concealment.
 * Monk finishing move: Dance of Clouds: 20% enhancement bonus to concealment. Works on friendly NPCs.

Some Area of Effect concealment miss chance are considered a physical bonus and are thus rolled separately from personal concealment miss chance.

Some examples of physical concealment:

 * Spell: Cloudkill. 20% AOE concealment.
 * Spell: Acid Fog. 20% AOE concealment (blocked by Freedom of Movement).
 * Spell: Obscuring Mist. 20% AOE concealment. Blocked by Blindness Immunity/Remove Blindness?
 * Spell: Stinking Cloud. 20% AOE concealment.
 * Spell: Incendiary Cloud. 20% AOE concealment.

Note: Miss chance due to being Incorporeal are also separate rolls from these sources, and thus stack.