I couldn't find it in the search and I don't see any signs of a closed asks so I'm going to ask, what can a mage of blood do?

An innate knack and knowledge for that which makes Friendship, identifying true friends and comrades, as well as knowing who’s likely to betray them! Maybe, like Kankri being the Seer of Blood, they’d also be able to Know information their ancestors or other Universe-selves knew? Of those related to them by Blood. Additionally, there’s the possibility of knowing where Blood is going to be spilled, that is, where Blood will be drawn, or has been drawn in the past.