Modifying the g-cube's engulf...
Engulfing Fog (Ex): A spectral cloud can simply move over Large or smaller creatures as a standard action. It cannot make a chilling touch attack during a round in which it engulfs. The spectral cloud merely has to move over the opponents, affecting as many as it can cover. Opponents can make opportunity attacks against the spectral cloud, but if they do so they are not entitled to a saving throw. Those who do not attempt attacks of opportunity must succeed on a DC x Reflex save or be engulfed; on a success, they are pushed back or aside (opponent’s choice) as the spectral cloud moves forward. Engulfed creatures are not considered to be grappled, but moving through the spectral cloud's space is similar to the effects of a solid fog spell. Each round a creature remains engulfed, it suffers xdx points of cold damage. The save DC is Strength-based and includes a +x racial bonus.