When you cast a blood
magic spell, you take damage equal to the blood required for the spell,
which you can draw as part of casting the spell (no additional action
required). This blood must come from you, unless you have features or
feats that allow you to use other sources of blood to power your
magic.
If you cast a Blood Magic spell at a higher level, the minimum hit points
increases to the level the spell is cast at.
You cannot spend more hit points than you have this way. (Kibbles Blood Magic)
