You’re caught off-guard—you can’t act or respond for a few seconds until you steady yourself.
Stunned is the status for when you get the wind knocked out of you by a fall, or when your head gets clocked by a flying chunk of metal, or when a combustionbender manages to cause an explosion right in front of your face. It represents those moments when you’re completely thrown off, unable to think or act with intent, until you manage to put yourself back together again.
Stunned leaves a character functionally helpless. The status never lasts for very long—no more than a minute or two at most—but that’s always long enough for a foe to take advantage. A Stunned character isn’t able to respond—even in the middle of a fierce combat—which means there’s no uncertainty when an enemy acts against them; the GM just says what happens.
Usually, Stunned is only inflicted by specific techniques and abilities. But Stunned can make sense if someone gets
a second time—perhaps by a strong strike from a blunt weapon or a blast of airbending—depending upon the actual fictional cause. Stunned can occur without warning or any other status if it makes sense in the fiction—for example, it might be the best way to establish the severity of a sudden blow from a hidden enemy.