You searched for killsurge
1. killsurge
Syntax: automatic
With this ability, the Diabolist fuels all summoned familiars with malice
and the desire to inflict suffering upon others, increasing the familiar's
hitpoints, damroll, and resistance to damage. This skill will automatically
have a chance to increase when the familiar is in battle in the same room as
the Diabolist. The higher this skill has been learned, the stronger the
spell will be. When the skill proficiency increases, the effects on the
familiar will also be increased automatically. If you switch subclasses,
the killsurge effect will be stripped from the familiar. Once you switch
back, the effect will be automatically re‑added to your familiar.