Signet's summoning magic: a life-ending sacrifice's blood animates her living tattoos into a monster battle squad.
Blood Magic is Tsarina Signet's summoning discipline. It requires a proper blood sacrifice: she pre-casts the spell over her swirling living tattoos, then when a chosen victim dies of a life-ending wound, all their blood flows into her and forms her 'Battle Squad' of tattoo-monsters — their power scaling with the quality of the blood. She may not bleed the sacrifice herself, so she captures two creatures, pits them together, guesses the loser, and casts on it before it's injured.
She can only summon once per night. Her plan for Carl was to charm him, have him die defending her, and use his rare Primal blood — but he took 'nary a scratch,' and the summon failed.
Signet's core summoning power and the mechanism of her trap on Carl.