GhazzyTV - Essence Drain & Contagion (or Bane/Soulrend) Trickster [SC/HC/Uber Elder/Shaper]

http://www.pathofexile.com/forum/view-thread/1640967

Poison

This build uses the unique dagger The Consuming Dark to poison enemies. The poison mechanic was overhauled in patch 2.1 and made poison based builds very strong. In this section I will try to explain the mechanics of poison and clear up why it is so good.

How poison is inflicted

To poison an enemy you need to hit it with a spell or attack that has a chance to poison. Only physical damage and chaos damage can poison. There are several ways to get a chance to poison, there is for example the Poison support gem which gives supported spells and attacks a 100% chance to poison enemies. There are also several nodes on the tree for this purpose, Adder's Touch for example gives crits with daggers a 30% chance to poison. This build uses the dagger The Consuming Dark. The line Your chaos damage poisons enemies translates to a 100% chance to poison for hits with chaos damage.
The keyword "hit" is important. Spells that do not hit cannot poison. This is important because Contagion does not hit and can therefor not deliver any "on hit" effects. This means while Contagion spreads the ED debuff it doesn't spread any poison. To spread poison you would have to use Bino's Kitchen Knife.

Why it is so good

As a general rule in Path of Exile, damage over time effects of the same source do not stack. This means if you spam Essence Drain on a boss he will take repeated damage from the projectile portion but he will only be affected by one DoT. Poison is an exception to this rule and that's one of the things that make it so powerful. If your chaos damage can poison then each cast of Essence Drain applies a new stack of poison. This means that poison naturally favors fast hitting attacks and spells, which Essence Drain is not. However poison still increases the single target damage of this build by a massive amount because poison just scales so well with all the stuff that also scales ED's damage.

How the damage is scaled

The base damage of poison is 10% of the initial hit's damage per second over the span of 2 seconds. Right now my Essence Drain hits for an average of 8.2k chaos damage. 10% of that doesn't seem like very much. But this is where the insane scaling of poison comes into play. Because poison is a damage over time debuff that deals chaos damage it benefits from all stats that increase chaos damage, damage over time and - if inflicted by a projectile - projectile damage. As I mentioned above in the special case of Essence Drain poison damage also scales with spell damage. The great thing is that this build already uses these exact same stats to scale ED's damage. This means poison gets to double dip on all these modifiers.
Here is an example with numbers:

Say you use a level 20 Essence Drain. At level 20 the projectile deals an average of 291 base damage per hit and say you have 100% increased Chaos damage from tree and gear and you support ED with a level 1 Void Manipulation (20% more chaos damage). The damage is then calculated as follows:

Initial hit = (291*2)*1.2 = 689.4 dmg

The base poison dps is 10% of that

689.4*0.1 = 68.9 damage per second

But now this poison base damage benefits from all the increases to chaos damage again. So instead of 68.9 dps you deal

(68.9*2)*1.2 = 165.4 dps

Your ED DoT dps would be

(809*2)*1.2 = 1941.6 dps

This means in this fictional example just one stack of poison results in a 8.5% increase of DoT dps. This number goes up as you add more damage multipliers because poison double dips on all of those.

If we take my actual damage as an example you can see the real strength of poison. As I mentioned above my ED hits for an average of 8.2k that puts me at 820 base dps for poison before any increases from gear or supports. As a comparison, the base DoT of a level 20 Essence Drain is 809 dps. With all damage increases and multipliers each stack of poison adds roughly 30k dps before curses/wither/profane bloom, there is simply no way to get that much damage anywhere else.