Many monsters and some weapons have a chance to inflict special effects upon their target when they perform a physical attack. This also applies to several combat, mystic and item skills.

These effects can range from simply increasing the damage inflicted by the immediate attack to inflicting status ailments, such as Poison, upon the target. Certain effects, such as Black Out, target single members of a union; others are automatically inflicted on the entire union if they hit any of its members. 

The possible effects are listed on the monster, weapon and arts pages. The special effects Added Effect Occurrence and Reduced Effect Occurrence raise or reduce the change for triggering an additional effect (done by respectively on your units).