I like the basic idea of this, though there is such a strong tension between the first and second ability that I worry about how it'd play out. Strategic tension can be good to a certain degree, but this one is very intense.
Agree with Inanimate here, this is a great basic outline, but I think the second ability wants to hurt me less as far as mana goes. I might suggest, for example, that it say "When you sacrifice ~, draw a card." so that you're likely to hit more land drops when you use it.
If this can draw a card at one mana, that'd be sweet. If it needs to be 1B to do that, well, that's still quite good: It also starts to fight with Exultant Cultist.I disagree the two abilities fight: You use the first ability to play your demon, and then the demon requires a sacrifice which you profit from.That does give me an idea for another alternative to life gain or card draw as the sack bonus: Put a +1/+1 counter on [your biggest] creature.
Bring Back Blood Pet 2016
"Whenever you sacrifice Demon Worshiper to a Demon ability, your opponent loses 4 life and you gain 4 life."