Draw Blood

-You reach your hand out to your target and their body flinches backwards. Their pores send blood swirling and rushing towards you meeting your hand and swirling around your arm. You deal damage and now can cast bloodmancy spells. You also gain advantage on all rolls against the affected creature. They gain disadvantage against all of its rolls to other creatures as well.

-Or you can draw blood from a blood vial. You reach your hand towards the vial and blood comes swirling out to meet you as it swirls around your arm. You can now cast bloodmancy spells.

-Or you can draw blood from yourself. You slit your wrist and use a pulling motion over your cut and blood is pulled out meeting your hand and the. It swirls around your arm. You can now cast bloodmancy spells.