How does Dark Tendrils work?

[uightpt]

Descriptive title is descriptive. I just floated a point into dark tendrils to see both what the complaints were about and whether it would be worth it anyways on a creeping darkness build, and it doesn't seem to do what it says it does. Most of the time, when I use it , nothing happens for one or two turns, and then the targeted enemy is pinned down, with a purple shadowy blob over it. Rarely, a trail of darkness reaches out, and when it touches them, it pins them down, with a purple shadowy blob over it. Also rarely, it does nothing at all, just goes on cooldown with no effect. What in the world is going on here? I can only assume that I don't know what the skill does, hence the patchy performance.

[Coldbringer]

I had a character with a ring that granted this skill. It seemed cool in the description but it's performance was crap. It's bad because it blocks YOUR view of the monster or group of enemies you're trying to fight. Doesn't seem to take effect or do damage right away either. Tooltips and performance should both be updated to make it a worthwhile skill to use.

[HousePet]

It creeps pretty slowly, so its not usually going to pin an enemy before you have killed it.