The Ring of the Black Cat is a ring that, whenever Plagg inhabits it, transforms the wearer into a black cat-themed superhero with the power of destruction and bad luck. The ring is currently owned by Adrien, who uses it to turn into Cat Noir.
The ring has a thick band with a circle surface surrounded by a lining with four pointed diamond shapes on each diagonal side. When Adrien isn't Cat Noir, the ring is silver and the circle is blank. But when Plagg enters the ring while Adrien transforms, it becomes black and a glowing green cat paw print appears in the circle. After Cat Noir starts running out of power, each toe of the paw print will disappear one at a time as an indication of how much power and time he has left until he turns back.
The Cat Miraculous grants its wielder incredible powers of superhuman speed, endurance, and strength. Its special weapon is a staff, which can be utilized as both a weapon and a communicator. Its special superpower is Cataclysm, which gives the user the ability to damage or destroy an object, like structures or metal bars. As long as the superpower isn't used, the wielder can remain transformed. However, as soon as the superpower is used, the wielder loses power and the transformation usually wears off in five minutes.
Legend has it that if the Ladybug Miraculous and the Cat Miraculous are used together, the holder will achieve absolute power.
In the theme song, the Cat Miraculous is in the raised center of the Miraculous jewelry box with the Ladybug Miraculous, both their sections creating a yin-yang symbol inside the box.
The Cat Miraculous is in the yang section. Some of the things that yang represents is heat, light, dominance, and logic.
Black cats are a symbol of bad luck, although they do symbolize good luck in some countries, like in ancient Egypt.
The ring can fall off while the user is transformed, which causes the user to revert back to normal.
In the original Ladybug PV, the ring has a very different design. It is entirely black with a cat face, the cat having green jewels as eyes and a red diamond-shaped jewel on its forehead.
Also, during the time the PV was produced and before the Miraculous theme was introduced, the ring brings bad luck to its holder — even when he or she is not transformed. Additionally, the ring can't be removed, but Félix is able to if he kisses Ladybug.
According to the official Miraculous Ladybug Tumblr blog, there will be more holders of the Cat Miraculous revealed.
If the person possessing the Cat Miraculous used it for evil, it would be "even more than [extremely dangerous]."