Bloody Double Mara could be improved in one of two very simple ways
1) Make the stat bonus identical to Bi-stat food, or;
2) Make it have no stat bonus at all, and not interfere with existing food. Simply reduce Vamp by 1 stage.
As it stands, my use of Mara is to use it to lower my Vamp, then eat another Bi-Stat food for the extra stats. It seems wasteful, it should either be as good as Bi-Stat or should not interfere with existing food.
BDM would still have value as a simple Vamp stage reducer even if it had no stat effect, but it probably wouldn't be gold standard. If it gave me Bi-Stat bonus and removed a Vamp effect, then it is worth keeping as gold standard.