Acid Fog

Creation [Acid]
Circle: Tactician 5
Casting Time: 1 standard action
Range: [Medium]
Effect: 45 ft radius spread of caustic chemical fog
Duration: [Encounter]
Saving Throw: Will; see text

This spell functions like obscuring mist, except that the area of the spell's effect can be centered on a target square within range, effects that inflict damage with the [Fire] descriptor do not remove squares from its area of effect, line of effect is blocked between two creatures if one or more squares of the fog exist between the two creatures, and for each creature, whenever that creature begins its turn inside the area of the spell's effect or the first time each [Round] that creature enters the area of the spell's effect, acid fog deals 2 damage with the [Acid] descriptor per level you possess to that creature.

Additionally, as a [Binding] effect, whenever a creature voluntarily enters or exits a square in the spell's area of effect using an action, it stops moving. A successful Will save allows the creature to continue moving, but it suffers a penalty equal to half its movement speed to its movement speed for that movement.