Diablo III- Skills Article LIX: The Demon Hunter, Passive Skills (4 of 5)

Numbing Traps: Enemies hit by Spike Trap, Fan of Knives, and/or Caltrops have their movement Slowed by 25% for 3 seconds.

Of inestimable use to battlefield-control Demon Hunters, the fact that this skill also affects Fan of Knives means that even other types of Demon Hunter (particularly damage-dealing or balanced Demon Hunters) will also have a strong affinity for this skill.  You do need to be careful- the effect is not as strong as the slows laid in by Caltrops to begin with, and is mostly useful for enemies that somehow leave the Caltrops areas in that event.  Applying this to your Spike Traps or Fan of Knives makes both of those skills into excellent secondary battlefield control, though, and lets Fan of Knives even act as an exit method similar to Strafe if you find yourself becoming surrounded- not a possibility to turn up your nose at.

Perfectionist: Reduce the Discipline costs of your skills by 10%.

Both evasive and battlefield-control Demon Hunters lean fairly heavily on their Discipline, so this skill becomes of high importance to them- if you’re operating either kind of Demon Hunter and you don’t have a third passive skill choice that helps your evasion or control (or benefits from either), then this is pretty much the only thing that really competes with Archery or Vengeance.  If you run out of Discipline with any frequency, give this a shot at filling a passive skill slot.

Custom Engineering: Your Caltrops, Spike Trap, Sentry, and Marked for Death skills all last 100% longer.

If you use these skills- any of them- regularly, you want this.  The only possible exceptions are if you use Marked for Death and none of the other skills, and always kill whatever you Mark before the Mark can run out, or if you use only Spike Trap and don’t have the Bandoleer rune.  Extending the duration and usefulness of your traps and your major enemy debuff are just too strong a set of effects to give up for anything that doesn’t flat out make you deadly.  If you don’t use these skills anyway, though, don’t bother- Caltrops and Spike Trap don’t actually change much in effectiveness if you’re not suited to them anyways, if you like something more than Sentry, you’ll like it more than Sentry anyways, and if you’re not the type to fling around a debuff like Marked for Death, you can’t really benefit from the duration anyways.

Grenadier: Grenades generates 2 extra Hatred, Cluster Arrow costs 10 less Hatred, and when you die, you drop a giant grenade that explodes for 450% weapon damage as Fire damage.

This is probably the strangest skill available to Demon Hunters.  Its assortment of effects is odd, particularly given how rarely you’re actually going to benefit from the death-grenade effect- it can’t restore you to life, after all, and you don’t gain experience while dead.  While this could do some interesting things for a Demon Hunter who’s heavy on party-friendly skills and also packs Grenades and Cluster Arrow, it’s unlikely to see a lot of use because of how quirky it is.