Unlike Innistrad's more ostentatious vampire families, Stromkirk vampires take pride in silence and subterfuge.

Stromkirk Bloodthief

At the beginning of your end step, if an opponent lost life this turn, put a +1/+1 counter on target Vampire you control.

Foundations

With House Voldaren ascendant, some members of the Stromkirk line took it upon themselves to "borrow" from the blood tithes.

Innistrad: Double Feature

Innistrad: Midnight Hunt

Stromkirk Bloodthief's ability cares whether an opponent lost life this turn, not how their life total changed. For example, an opponent who gained 2 life and lost 1 life in the same turn still lost life.