OK; I know that its been done before, but here is my take on a blood knight conversion. This is a trial figure to see if the idea is feasible. If it works than just four more to go to make the unit...
It starts with the head of a ghoul (on a pin). Add to the body of a Dark Eldar Warrior and the arms of a cold one rider..
Take a Chaos knight horses head and remove the solid bit under the head so that the reins hang free.
Use the hair of a dark Eldar warrior as a tail on the body of a chaos knight horse (Which has had the Chaos symbols scrapped off).
Attach Cold one rider legs and the body to the horse and to have the start of a blood knight..
I had to raise his body quite a lot to keep his proportions looking correct. This means that I will need to green-stuff him a waist. That in itself is not a major problem. The biggest worry that I have is that the horse is just so very large that the rider looks a little comical and lost on its back. Maybe if I give him a tall hat and cut off the horses spikes then the proportions might look better. For now I will let him sit on the shelf for a small time to see if I am happy enough to continue.