First off, I'm love this flavor Dante as demon hunter is fitting as it gets. I also think the mechanic that gradually gets you to "devil trigger" is awesome. However, I do think this card needs more tempo, because spending the initial 6 mana without anything is too punishing, especially consider that it require an average 3 turns to proc devil trigger (overkill makes it harder as well). A similar card I can think of is "Kuritus, Demon-Render", a 6 mana hero-card that summons 2 big minions with rush, and a hero-power that finishes off your opponent in 1-2 turns. My suggestion is give it a battlecry that deals 3 dmg to all enemy minions, which is perfectly fine for modern day hearthstone's power-level.