Percentage is an estimate based on tests by players. The game does not display the actual formula.
Confuse works similar to Polymorph. When trying to inflict confuse, player's effective attack strength is given a 50% boost and then compares it to the effective defense strength of enemy target. If the 150% effective attack is greater than target enemy 100% effective defense, then the enemy is confused. If it is still not enough, then the target will resist your spell. Neither the caster not the target is damaged regardless of outcome.
While under confused status, the victim can hit themselves while using a token to perform an action. If the effect triggers, they will have their action blocked and damage themselves by 40-60 health in the process. Their target enemy or ally will take 0 damage. They will also only receive 50 points should this happen. They can get lucky and not trigger the effect until they exhausted their rounds or unlucky and hit themselves every single time under the spell until it is removed.
If trying to cast Cleanse to remove the debuff, if confuse triggers, cleanse will not be casted.
Confuse does not stack with another confuse. Should confuse be inflicted again before the first confuse's duration ends, the first confuse set-up (% chance to trigger) is discarded and the new confuse set-up is applied. This means that even if the initial confuse only has 1 round left before being automatically removed, the second application will get full rounds.
Confuse is a spell type action so bonus damages like Poison, Leadership or Backstab will not trigger when trying to inflict it. It can also be used to lower Confidence bonus damage. It does not use up a Polymorph spell when inflicted if the target is under poly status. It also ignores Mana Shield and Sentinel when trying to inflict the debuff.
If the victim is stunned or becomes stunned due to confuse effect, the action will appear in the battle stun log.
Confuse cannot be performed if the caster is defeated or stunned.
Confuse can be removed with the Cleric power Cleanse.
Syren increases the chance that confused opponents hit themselves, from the base 20% to 20% + 2.5% per Hero Level. The effect triggering is still based on chance but if you are going to inflict Confuse, do so with Syren unless you need a better attack boosting general such as Xira or Evalice to successfully apply the debuff. Can be purchased through Oracle upon reaching Level 260.
Ephraline's ability is weaker as she only adds 1.5% per Hero Level chance for the confuse effect to trigger. However, the hero has a secondary ability of adding +2 damage to the innate gate burn ability of mages. Ephraline is a good substitute in case players cannot be bothered to swap heroes should they decide to switch from attacking (and add gate burn) to casting confuse or vice versa. Can be purchased through Oracle upon reaching 320.
Confuse is mainly used to halt the attacks of enemies. When players are inflicted by Confuse, they will either ask for an ally cleric for a Cleanse or patiently wait stock tokens so that they exhaust the debuff and unload unhindered attacks fast before another Confuse hits them. This can be useful in trying to delay the offense of the enemies and give teammates some time to regroup to cast Heal and set-up Revive and maybe Sentinels.
It can be used in the guild based Arena to limit the points an enemy can get in a battle, thereby losing ground in the standings and be behind a rank cutoff. This may force them to buy or use a refill to compensate.
Confuse is another great skill for mages, almost unfair. Player have the points advantage (Arena and Guild Coins) as well as a huge attack boost to successfully inflict enemies they can't normally beat in a straight duel. The infliction and trigger for targets to hit themselves is not guaranteed to work 100% of the time as it still relies on player stats and chance respectively. But it sure can annoy the heck out of the enemy team, especially in the Arena.
The picture in the ability is general Noktar and energy swirls from Jahanna.
There is discussion in the forums on the % applicable for confuse, in that while the description of this spell is at 20% that in reality it is a higher number, on the order of 40 or even 60%, with some basis on statistical evaluation. Combined with a confuse general this can result in the observations that 100% confuse rate seems to be possible and occurs too many times for a simple probability discussion.