Needs review
Source: Dragon Magazine #358

Description: Your spells slam their targets with irresistible force.

Prerequisites:

Only spells that target one or more creatures can be made forceful. An opponent struck by a forceful spell must make a Fortitude save at the same DC as the spell or be knocked prone and stunned for 1 round. If the spell affects more than one target, the forceful effect affects only one target (of your choice). A forceful spell uses up a spell slot one level higher than the spell's actual level.