I think I can see quite a few problems which will occur in the use of this but the most standout ones I think are:
Only affects vampire units in the map from the start.
Goes up to Level 10, no further which might be wanted.
your explosion on death might fail if there are 2 or more vampire units in the map as you pick a random one from the group.
you appear to be using many many many vampire units, but I dont see how this is neccercary all it means is alot more work for mapmakers in the object data, it's unlikely they'll want to make 9 variations of the same vampire to use this.
thats all I have atm