Silverquiet

A grieving face shut inside a case of hammered silver by hands that no longer exist. While the case holds, almost nothing you land actually reaches it, and the cold silver drinks the force out of the one big swing you were saving for it — and more than force: the omens you seal against a later hour it drinks straight through the silver, six of them gone each turn (Omen Eater 6). Break the silver and it stops defending entirely, because what has been waiting in there does not need armour.

The sealed case. While the silver holds, almost nothing you do reaches it, and the cold silver drinks the force out of the one big swing you were saving. When it finally splits, the thing that was waiting in there is very hungry and no longer armoured, and it does all its killing in the open.