Radiance

Enchant target creature you control. Whenever
your life is 10 or less, you may sacrifice that
creature. You'll gain life equal to the sacrificed
creature's converted mana cost.
Healing Church Covenant (enchanted
creature has "Executioner" added to its subtypes,
except if it is an Vileblood).
"The executioners despise the impure Vilebloods, and
no matter what the circumstances, would never
cooperate with the bloodthirsty hunters who serve the
undead queen, Annalise."