Unleash

An Unleash is a special attack most Artifacts and no standard weapons can perform. Only artifact weapons have unleashes, but not every artifact has an unleash. You have no control over when an unleash is triggered; if you have a weapon equipped that has an unleash, then after selecting the attack command, you may instead get a message like this one: "Ivan's Masamune lets out a howl! Rising Dragon!"

When an unleash occurs, a new attack animation sequence is triggered, instead of the usual jump/slash enemy. Each unleash has a different animation sequence, and no two weapons have the same unleash.

An unleash has a certain percentage attached for the unleash to occur. Most weapons Unleash at a base rate of 35%, but some have a higher base rate. The rate of unleashing can be altered by equipping certain equipment.

Some unleashes have a special effect, such as instantly downing the target, afflicting enemies with status conditions, replenishing HP or PP, or multiplying base damage two or three times.

Every unleash is both a physical attack and connected to an element; the damage done is calculated by comparing the Adept's Attack rating to the target's Defense rating, just like a normal physical attack, then the Adept's Power with the element in question is compared against the target's Resistance to that element to determine how much the resultant damage is modified for better or worse.

A full list of weapons in the Golden Sun series that have unleashes can be found here.

Although no real explanation for unleashes occurs in-game, a small bit of easily forgotten text on the subject appears when Isaac's party first arrives in Kolima, prior to having defeated (and healed) Tret. The enraged tree curses the residents of Kolima for taking their axes to him, turning them into trees, so that they would die alongside him. Isaac's party happens to get involved, needing to pass through the Kolima region as part of their quest. Immediately they are set upon by Tret, who immobilises the Adepts, pinning them to the ground. However, as the wave of Psynergy that would turn them into trees approaches, the Adepts are enveloped in a shimmering barrier that wards off Tret's curse. This barrier was a purely reactive and subconscious display of Psynergy, as none of the Adepts intentionally used their powers to create the field. They assume this type of subconscious defence is similar to a weapon's unleash, which holds vast, though uncontrollable, power. Apart from a concluding remark about how it would be nice to control this ability, it is never mentioned again. As such, this only serves to confirm that the Adepts do know that unleashes exist and that they are uncontrollable and nothing more.