Miasmic Cloud

Least Invocation; 1st
A misty cloud of fog spreads in a 10-foot radius from you when you use this invocation. The fog does not block line of sight, but all creatures in the fog have concealment. Any creature (other than you) that enters the fog must make a Fortitude save or become fatigued. This effect lasts as long as the creature remains within the cloud and for 1 round thereafter. A moderate wind, or any fire larger than a torch, immediately disperses the fog. The fog otherwise lasts for 1 minute.

Source: Complete Arcane