Explosive Spell( Unapproachable East, p. 43)
You can cast spells that blast creatures off their feet.
An explosive spell ejects any creature caught in its area to the nearest edge of its effect and knocks the creature prone if it fails its saving throw against the spell. For example, an explosive fireball moves all creatures in its area who fail their saves at least 20 feet from the center of the effect, while an explosive lightning bolt moves targets 5 feet to either side of the stroke. Any creature moved in this manner takes an additional 1d6 points of damage per 10 feet moved. This movement does not provoke attacks of opportunity. If some obstacle intervenes to prevent the blasted creature from moving to the nearest edge of the effect, the creature stops at the obstacle but takes 1d6 points of damage from striking the barrier (in addition to any damage taken from being forcibly moved to the barrier). Explosive Spell can only be applied to spells that allow Reflex saves and affect some area (a cone, line, or burst). An explosive spell uses up a spell slot two levels higher than the spell's actual level.