The Copper Mirror is a mirror that Meng Hao got tricked into picking when he first joined the Reliance Sect. In the past the Copper Mirror had been broken into eight different shards.
During the war of the Mountain and Sea Realm and the Immortal God Continent, Devil Realm, and the 33 Heavens it was revealed that Lord Fifth is actually the spirit of the Copper Mirror. As Meng Hao became more powerful he learned that the Copper Mirror was actually a battle armor created by Patriarch Vast Expanse that was shattered into eight pieces by Allheaven.
It was an item that Meng Hao was tricked into picking up. Later he found that it can explode the butts of demon beasts that have fur, and not to soon after he accidentally found out that in exchange for spirit stones it can duplicate any item.
Later on in the story we find out from Meat Jelly that Lord Fifth is sealed within the mirror. When Meng Hao was within the Demon Immortal Sect, within the fourth plane Meng Hao used the copper mirror to "absorb" the entire continental mirror, subsequently leading to True Spirit Night's awakening.
When Meng Hao was close to awakening his Allheaven bloodline, Lord Fifth reveled that when Meng Hao becomes an Allheaven Dao Immortal he will be capable of transforming the Copper Mirror into its Battle Weapon Form.
Copper Mirror (Base/Incomplete form)Edit
While in the Copper Mirror Form it has the ability to duplicate anything as long as enough spirit stones or immortal jades are given. In the earlier stages of the story it also had the ability to affect beasts that had either fur or feathers.
Battle Armor (Complete form)Edit
At first Meng Hao was only able to use the Battle Weapon which was just a blade that covered his hand due to the Copper Mirror being incomplete, but slowly as Meng Hao retrieved more shards of the Copper Mirror it started taking shape of armor that covered his entire body.