Randy discovered something interesting about his ability as he siphoned his enemy's blood, and that was how he managed to suck in all of the black-cloaked vampire man's blood into his body.
This was something that should've been biologically impossible, as he couldn't possibly have the capacity to store two people's blood within himself.
Even if the blood-cloaked vampire man's blood volume was less than his, which was unlikely, he shouldn't have been able to absorb all of it. This was because he still had an ample amount of blood in his system.
While he had lost some blood before in his previous fight with the demons, he hadn't lost enough to warrant his feat of absorbing the black-cloaked man's blood completely.
Moreover, there were the scientific aspects of the problem, which needed to be taken into consideration, such as blood type and compatibility. Otherwise, there would be some complications.
