Stun

Stun is a common status effect preventing affected characters from taking most action, including blocking and tagging out. It is perhaps the deadliest effect in the game when fully exploited, as it leaves the affected character vulnerable to the full damage of attacks, critical hits, and the enormous damage bonus of the Cloak of Destiny against stunned opponents.

Mechanics
There are some relatively intricate mechanics regarding this status effect, as stun lasts always last for a set duration of time (_ seconds) or until an attack or attack sequence is completed on the stun character beforehand. It's thus more volatile than other effects that tend to last for a set amount of time absent tag-out.

Stun Chance
Most stun affects cannot trigger on blocking characters. (Cloak of Destiny, Bane/Luchador are exceptions?)

Stun Duration
Stun always last for _ seconds or unless an attack or attack sequence is completed on the stun character. However, if that attack has the capability to stun, the stun condition can be renewed.

Characters and Effects That Employ Stun
Stun chance is found on the moves of different characters, on a few different characters' passives, and on various gear pieces, including the aforementioned Cloak of Destiny. When stun is found on a character's move, there is usually an associated 50% damage penalty, meaning that the move does 10%~16.5% of the character's damage stat (depending upon upgrades) as a base.

Characters With Special Attacks that Can/Will Stun

 * Batgirl's SP1: Batgirl (both Batgirl/Prime and Batgirl/Cassandra Cain) is the one character to have an 100% intra-special stun. An intra-special stun would be useless otherwise
 * Batman's SP1:
 * Static's SP1: Static's SP1 attack will always stun the target when it goes unblocked. Moreover, this attack has no associated damage penalty.

Unsorted
Batman/Insurgency's basic attacks deal 300% increased basic damage against stunned opponents.

It is not possible to deal combo enders on a stunned opponent. An exception is Static.

Red Son Green Lantern and Beyond Batman's passives provide immunity to stun, including stuns caused by Martian Manhunter or Luchador Bane's passive. Previously these stuns will ignore immunity, but this was fixed in an update.

Characters than can stun are Luchador Bane, Batman, Cyborg, Hawkgirl, Martian Manhunter, Prime Solomon Grundy, Static, New 52 Flash, New 52 Green Lantern, Killing Joke Joker, Zatanna (self-stun only). Red Son Solomon Grundy and Regime Green Lantern.

Batgirl has visual stuns at the beginning of their Special 1, Art of Deception, but since it is the beginning of a special it only serves to trigger Cloak of Destiny.

Trivia

 * It is possible for a freeze special to apply stun through stun gear; there seem to be two outcomes when this happens: both "Stunned" and "Frozen" appears, and the freeze animation is played, or only "Stunned" appears and the stun animation is played. The bonus damage only applies in the latter case.