Hindering Blast

Warlock Invocation
Level: Least, 2nd lv.
Components: V, S
Casting Time: 1 standard action
Range: Self
Duration: Instantaneous
Saving Throw: None
Spell Resistance: No

You transform your eldritch blast into a hindering blast. Any living creature struck by a hindering blast must succeed on a Will save or be slowed for 1 round in addition to the normal damage from the blast.

(Complete Mage, Page 124)