Mournful Casket

If an ally has been put into your graveyard this turn, this gets +1

.

Temper

Rulings

From the Compendium of Rathe release notes

Mournful Casket’s ability generates a conditional continuous effect that is always checking. If an object with the ally subtype has been put into your graveyard at any point during this turn (e.g. destroyed from the top of your deck, discarded from your hand, destroyed while it was in the arena, etc.), Mournful Casket will get +1 for the remainder of that turn.

Keyword notes

Temper - Temper is a new keyword that exists on equipment in Crucible of War. Usually high in defense, Temper equipment presents a choice when it is down to 1{d}, of whether to defend with it one last time and see it destroyed, or save it to use for its ability.