Being stunned or dazed is a special condition that leaves a character immobile for a short period of time. When characters are stunned, they are left dazed for a few seconds and can not perform any action. The only ways for a character to get out of this status is by waiting, by getting hit, or by button mashing to reduce duration. It is accompanied with a cartoony tweeting sound effect that loops until the condition has stopped.
The only known cause of stun is shield breaking.