Well, not to be too critical, but, if you didn't have 6 drain lifes in your deck all ready, wouldn't you rather have a drain life than a Horrify 90% of the time. Drain life is never a dead draw. Drain life has a good chance to be card advantage neutral. Drain life even grants you some life.
Just saying, if I was building a deck, I would find this card as is, to be to weak to be included. Darkness just has a ton of stronger cards to choose from IMHO. Like I said, I think it could use a bump in power. Maybe a -1/-1 on the creature would be enough. (as though the creature was so scared it aged 10 years)
Again, love the card. Great idea. Just needs a little more umph to compete for a card slot IMHO.