Shadow of Blasmophet (Red)

When this attacks, draw a card then discard a random card. If a card with 6 or more

is discarded this way, search your deck for a card with blood debt, banish it, then shuffle.

Blood Debt

Rulings

From the Monarch release notes

You cannot defend with Shadow of Blasmophet as it has no defense value. (This is different than if the defense value was 0.)
Nobody has priority during the resolution of an ability. For example, you cannot play or activate an ability after drawing the card but before discarding nor can a player respond between you drawing and searching your deck. Players should respond before the ability resolves as you cannot do it during the resolution.
The card this searched for must have the keyword blood debt. Cards that reference blood debt do not count unless they also have blood debt.
You may elect to banish nothing, however the search is mandatory if a 6+ card is discarded this way and therefore your deck must be shuffled.

Keyword notes

Blood Debt - Blood Debt is a new keyword existing on Shadow cards. Shadow cards can inflict a loss of life to access a greater power. At the end of your turn, you lose 1{h} for each blood debt card in your banished zone.

You only lose life at the end phase. Players do not have priority during the end phase.
If you have multiple cards with blood debt, you lose 1 for each instance of blood debt at the end of turn.
Only face-up cards banished with blood debt counts and will lose you . Face-down banished cards have no effects or stats.