Least Invocation; 2nd; Eldritch Essence
This eldritch essence invocation allows you to change your eldritch blast into a frightful blast. Any creature struck by a frightful blast must succeed on a Will save or become shaken for 1 minute. A shaken creature struck by a frightful blast is not affected by the shaken aspect of the blast but takes damage normally. Creatures with immunity to mind-affecting spells and abilities or fear effects cannot be shaken by a frightful blast.
Source: Complete Arcane