Demonic Empowerment

It seems like you've missed a few spaces on this one. (are you going to edit those out?)

A decent riff off of Angelic Destiny, although I think "Vampiric Empowerment" seems more fitting considering what the card actually does. Lifelink is more representative of Vampires moreso than any other creature type, even non-black ones.

If the flavor you're trying to capture here is that "the creature has sacrificed another of your creatures for demonic power" Then I'm not sure why it's physically becoming a demon itself. There's a difference between serving a demon for it's help and asking a demon to physically make you as powerful as itself.