Diablo III- Skills Article XLVIII: The Demon Hunter, Hunting Skills- Marked for Death

Marked for Death (3 Discipline): You mark the selected enemy.  For the next 30 seconds, they take 12% more damage from everything.

Marked for Death is an amazingly useful skill, particularly given the tiny Discipline skill.  The base form is best used on single large enemies- trying to stick it to everything when you’re fighting a larger number of enemies is an exercise in frustration and futility, and will eat all your combat time trying to make sure everything is taking more damage, rather than actually dealing out that damage.  That said, the damage boost is very nice, and if you use this in a party, it just keeps getting better.  Definitely a prime pick for most Demon Hunters.

Contagion (3 Discipline): You mark the selected enemy.  For the next 30 seconds, they take 12% more damage from everything, and if they are killed this mark gets copied to 2 other enemies nearby (including this effect).

Contagion makes Marked for Death useful no matter how many enemies you’re fighting- the rune’s effect is useless against bosses, but effectively infinite spreading of the mark as long as enemies are nearby makes things incredibly simple- just lay one mark at the start of each fight, and most things should be marked before long- there is no limit to how much Contagion can chain, after all.  Very useful, and a prime pick.

Valley of Death (3 Discipline): You mark a 12-yard radius circle.  For the next 15 seconds, enemies within it take 12% more damage from everything.

Unless the enemies aren’t getting anywhere near each other and you’re having to ‘train’ them individually around, there’s really very little reason to use this instead of Contagion.  The effect is shorter, and despite the nicely sized area, you don’t really have the kind of location-control over enemies to keep them in it.  It could be used in conjunction with a Wrenching Smash/Call of Arreat Barbarian or a Cyclone Strike Monk if you’re really worried about getting everything marked quickly enough, but as long as things are dying, why do you care that much?  Use Contagion.

Marked for Death (3 Discipline): You mark the selected enemy.  For the next 30 seconds, they take 12% more damage from everything.  12% of the (unenhanced) damage dealt to the target is dealt as additional damage to every enemy within 20 yards.

This is a bit of a weird rune.  It makes some sense- tack this onto a single rare mob or a unique enemy just before your melee pal starts beating on it, and watch things drop around them just by proximity.  However, it really only is much good in that sort of a situation- and those aren’t as common as encountering groups of Champions or large clusters of regular mobs, since most Bosses are fought alone.  While it’s neat conceptually, Contagion just flat out stays stronger and applies more often.

Mortal Enemy (3 Discipline): You mark the selected enemy.  For the next 30 seconds, they take 12% more damage from everything and your attacks against them each restore 3 of your Hatred.

One of the two premier forms of Marked for Death to use against bosses, Mortal Enemy is most useful if you’re fighting a boss alone or with only one friend.  This is especially hilarious if you use it conjunction with Rapid Fire or another skill that has a very low per-attack Hatred cost (like Strafe).  Should you find yourself facing a boss from a save position, this will let you dish out horrifying amounts of damage and laugh all the way to the end of the battle.

Death Toll (3 Discipline): You mark the selected enemy.  For the next 30 seconds, they take 12% more damage from everything and anyone attacking them heals by 1% of the damage dealt to the marked enemy.

Barbarians and Monks will love you for this.  On the surface, a 1% drain doesn’t seem like a lot, but a lot of Barbarians and Monks will be desperately scraping together a measly 4-6% to keep themselves in one piece as they soak up hits and swing back at attackers.  This rune is therefore in a close contest with Mortal Enemy for ‘best anti-boss rune’.  It really comes down to whether you’re traveling with a bunch of melee artists or not- the kind of damage they can take beating up a boss at that range is usually pretty devastating, but on the other hand, if you pump out even more damage via Mortal Enemy, the enemy will die that much faster.