See also: Spell Combinations: Shockwave

Codex text

An adventurer beset from all sides may find solace within the temporary confines of a Force Field spell, which temporarily protects aganist all damage. Since the spell also prohibits movement, however, the original situation will still persist once the spell fails. If a mage casts Crushing Prison atop the Force Field, the contradictory effects will result in a spectacular disintegration of both spells, generating a shockwave that harms all in the area except the original subject standing in the epicenter.

Further information

Damages and knocks back everyone except force-field target, very hard to resist. The combo can only be achieved on an enemy unless an ally is already under the effect of Crushing Prison, as cast by an enemy mage.