Notable Passives:

1. Crimson Gluttony [5/5] - Arguably the most important node on Base Class Tree, it increases Health Regen which is one of the most important stats in this build
2. Stolen Vitality [8/8] - Increases your Vitality, which grants Health and Health Regen

Lich Skill Tree (86 Points)

Notable Passives:

1. Survival of the Cruel [8/8] - grants you more Health, and some Spell Damage Leech
2. Apocrypha [10/10] - take it for more Intelligence, which increases the damage of Aura of Decay, and for Mana Regen
3. Reaper [5/5] - Your Damage instantly kills enemies below 10% of their maximum health, which is especially useful when fighting bosses.  It synergizes greatly with Damage over Time.
4. Lasting Stench [8/8] - Passive which increases your Poison Damage and Poison Duration, Poison being the main type of damage the character is dealing
5. Crippling Insight [8/8] - +16 Intelligence equals 64% increased Aura of Decay Damage and 16% increased Poison Effect, the downside - less Health Regen is worth the sacrifice
6. Unclosing Wounds [8/8] - damage increased by staggering 112% at the cost of 8% of Current Health Drained Per Second, which is not much considering all the Healing Effectiveness of this Character
7. Three Plagues [8/8] - this Character will in fact benefit only from Poison Penetration, nonetheless, it is still a powerful Passive
8. Contagion Engine [5/5] - you deal 100% more DoT if you killed an enemy recently, which is a common occurrence
9. Soul Maw [5/5] - increased Health Leech and increased Damage Leeched as Health

Lich Passive Tree has many completely useless for your purposes Passives and some that are specifically there for you to take. Look for Health and Health Regen - these are the most important stats, Poison Damage, Damage over Time, Intelligence, and Health Leech are desirable as well. Minion, Critical, Ward, Necrotic and Bleed-related Passives are not really useful, don't take them.
Symbol Of Decay would be useful if not for the fact the Shield offers potentially great stats. Elixir of Death is a good candidate to invest some points in if you struggle with Physical and Necrotic Damage you take, and if you have high enough Health to sustain the constant damage. You can skip on Passives such as Wraith Bringer and Reaper if you feel like investing these points somewhere else. One Point in Volatile Blood gives you less Health Drain, you can put some more points there.

Aura of Decay - This is the main source of damage in this build, it's an Aura that deals Poison Damage over Time to surrounding enemies and to your character as well. To combat its effect on you, try to cap your Poison Resistance and get as much Health Regen as you can, invest four points in Absence of Life as a defensive measure. Plague Rat increases the AoE of the Aura so it helps with clear speed, Bubonic Aura helps with it even more - it inflicts Plague that deals damage and spreads between enemies, Corruption makes enemies capable of exploding on death, dealing Poison Damage. Rot Weaver, Mana Blight, and Poisoned Soul increase the damage by allowing the Poison from Aura of Decay to activate 104% more frequently. Loathing will increase the damage, it has an 8% chance of applying Mark of Death on an enemy that hits you - enemies with this debuff will take 30% more damage for 8 seconds. You could invest some points in Poison Skin, it's really good for when you're fighting with tough enemies, but it can backfire as well. Poison Bolts could be useful, but it requires too much of an investment. You can forfeit Bubonic Aura, the Plague it inflicts will not be as powerful as the Plague caused by Spirit Plague, and these debuffs don't stack, however, it's still a good Passive as you won't use Spirit Plague all the time. Note that Aura of Decay is not a Spell, increases in Spell Damage won't affect its damage.

Reaper Form - It's a buff that should be on constantly, it makes you lose Health over time and cripples your Health Regen. Soul for a Soul and Reaper's Curse are highly offensive Passives, you sacrifice 40% of your Healing Effectiveness and you lose 2% of Health on Kill, but increases your damage by 180%. Mistress of Decay makes you deal more DoT, but you need to give up 40% of your Health Drain. Harbinger of Blood increases Health Leech and Healing Effectiveness by 40%. Blood Tethers gives you a chance to activate Blood Tether when you're hit, healing you with great efficiency. Reaper's Ascendance grants you a stack of a buff with the same name that you can have 25 of - it increases your Spell Damage by 50% at its full potential. If you have high Intelligence - take Soul Shroud for more Armor and Vile Shroud for more Poison and Necrotic Resistances (if you need any). Another Potential candidate is Death Comes Quickly, it's however very inconsistent and not that helpful during boss fights.

Transplant - A mobility Spell that lets you teleport at the cost of your Health. Invest your points in Bone Armour for greater defensive capabilities. Go for Pale Mind for a better Mana sustain and take Sadism that is already on the way for more general damage. Reign of Blood is there just for a minor damage increase.

Spirit Plague - A Curse DoT Spell that has the potential of greatly increasing your damage. Go for Endless Decay and take every Passive on your way there. It increases your DoT, your Poison Damage and now it will also inflict enemies with Plague - a debuff that works in a similar fashion to Poison, but it doesn't stack. Take Toxic Transmission, since you're specialized in Poison Damage. Efficacious Application and Perpetuity make this Curse last longer and more convenient to use.

Wandering Spirits - These Spirits will provide a small damage boost. Spectral Putrescence is by far the most important Passive there, Spirits now have a chance to fire a projectile that deals Poison Damage each second, and with the amount of Wandering Spirits, it's a very consistent and reliable damage source. Take the two passives nearby to increase its effectiveness. Lingering Souls, Thin Veil, and Spirit Swarm are important Passives as well, take these to increase the duration of this Spell, and the number of Spirits, which are the most efficient upgrades by far. Infectious Death will convert the base damage of this Spell to Poison, which is the type of Damage this build deals.

Stat priority:

For this build, you want to focus on increasing your Health Regen, and Poison Damage - Poison Damage and Damage over Time are the most efficient ways to size your damage. Spell Damage will increase the damage of Wandering Spirits, Transplant, and Spirit Plague - these are not your main damage sources, but they will increase your DPS nonetheless. Healing Effectiveness and Health are the main defensive layer of this build, you will be constantly drained out of your Health due to the configuration of your Skills, so it's extremely crucial to look for it on your gear. Intelligence is an Attribute that increases your DPS. You should look for: 

1. Increased Healing Effectiveness
2. Damage over Time/Poison Damage
3. Health
4. Intelligence
5. Vitality
6. Endurance
7. Leech
8. Spell Damage
9. Resistances

Recommended Unique Items: 

Woven Flesh  - This Unique Armor is a must for this build. It allows you to sustain your AoD and Reaper Form for much longer by providing various Health Leech-related bonuses (Overkill Damage Leeched as Health, Health Leech increase, Health Leech Rate Increase). 

Atrophy - An offensively-focused set of gauntlets that provides a very high Damage over Time increase, Time Rot Duration Increase, and gives you an additional chance to Slow Enemies which helps you escape them. Moreover, Atrophy also increases the Global Slow Duration which has some nice synergy with the build. 

END NOTE

This is the beta version of our Poisonous Aura of Decay Build for Last Epoch. We didn't have much time for testing, but this build already shows a lot of promise and outperforms many other End Game setups. Obviously, as the game gets new content updates, we will be updating this guide regularly, though it may be impossible to be done after each Patch.