Hello.
This bug has been reported in the past : Rip blood / carrion hunger
As my others spell, Rip Blood goes unusable when I am out of mana. So this node does not work.
Moreover, and I guess it’s a another bug, if you look at my mana cost of Rip Blood, I am at zero. At zero, I guess I should be able to use this spell even without Carrion Hunger node. But I can’t.
Edit : I removed Carrion Hunger. And I CAN use my RIp Blood spell (which cost zero) now. I guess there is a bug in the interaction of Carrion Hunger and the already zero mana cost of my spell.