I just looked at BLOOD, I think I might pick that one up… somewhere. lol.
In my game, I’m thinking of unlocking new powers over time, but not really incorporating RPG elements. I have boosts system though. If you over fill on blood(drink to greater than 100 points), you go into a “blood rage” that gives you invulnerability, speed and power boosts, until your blood lowers back down due to time and/or damage.
The trade off is that you have to drink a couple living people to get there(blood packs just won’t due), which will put you on the top of the human hit list.