Immune: construct, ooze, plant, undead

A stunned creature drops everything held, can't take actions, takes a –2 penalty to AC, and loses its Dexterity bonus to AC (if any).

Marius, Scholai Armsmaster Says: Stun effects usually grant a Fortitude save, which makes them ideal for locking down squishy opponents like wizards, rogues, and fey. The stunning fist ability does not grant spell resistance.  If a wizard cannot get through a monster’s magical defenses, there is a good chance that a monk can.