Source: Bestiary 4, pg(s). 130
Blood golems are a type of golem brought into animation from gallons of alchemically treated blood. The golem itself is not locked into any particular shape or form and can move about like an ooze, or take the shape of any creature its size, by coagulating its blood to make a type of skin or coating.
The blood golem attacks its opponents by hardening its outer surface and pummeling them with tremendous force. These attacks also have a secondary affect of attempting to pull additional blood from the victim. If successful, the golem can in essence heal itself. However, the golem is also susceptible to attacks that leave gaping wounds in its outer shell causing it to leak its own blood.
The golem's body is crafted from only fresh blood of at least 20 medium creatures or humanoids and then mixed with a series of alchemical concoctions of 500g gp worth.