The Claw of Mirmoggin

The Claw of Mirmoggin is a ring that Finnick often uses in conjunction with his powers. The rings were originally supposed to be worn by werewolves, according the Dalton Wood. It is essentially a magical suppression device, design to keep supernatural creatures under control. Though it is insufficient in fully suppressing Finnick's power, Finnick seems to use it to keep the Aspect of Death under control - without it, it seems likely he'd destroy himself.