The Tyrant's Claw

From Inga no Kusari wiki

The Tyrant's Claw is Hydriatus' dormir.

With the loss of his left arm, Zamael Hydriatus created the skeletal claw as a replacement, formed from a shard of Nexus Tempest's Hollow mask. It is slightly oversized for the arrancar, but has effectively replaced his left arm. It is grafted onto Hydriatus' flesh at the shoulder, and is completely exposed to sight. There are no muscles or tendons or even skin on the arm, just bone.

Dormir Ability

Cero Negation: The Claw was developed to cancel out one of Hydriatus' most glaring weaknesses – his lack of Cero defense. Now, the skeletal arm is capable of neutralizing opposing Cero by projecting Hydriatus' Cero into a shield around the palm of the claw. This acts as a Hierro which only deducts 30 pts from an attack which involves Reiatsu.