Moon's Caustic Arrow Occultist Build Guide (PoE Necropolis 3.24)

Due to the latest balancing changes, we do not recommend playing this build anymore, as it does not meet the high standards we apply to our guides in terms of fun and performance. We are leaving it up as a reference and it might be revived in a later patch.

Introduction

This guide proposes a character that is a very affordable bow-wielding Witch, focused on very high defences and quick large-area clear with Caustic Arrow.

Builds in the chaos damage-over-time archetype often have a difficult time scaling into the late game. Caustic Arrow, however, can powerfully leverage just a few scaling mechanics while becoming a defensive powerhouse, which enables it to tackle virtually all map content in the game, whereas nearly all other builds must avoid certain modifiers.

Despite the Witch ascendancy classes having no inherent access to bonuses to bows and bow skills, Caustic Arrow stands apart from other bow skills, with spell-like scaling through extra skill levels and jewels. While the guide suggests easily obtainable and powerful unique options in its item sets, it relies on no specific unique items for its core functionality and most rare items suggested by the guide can be crafted by you eventually.

The gameplay is of moderate intensity, cruising through the majority of map content, with a slight ramping up of button presses for weakening tougher enemies and dishing out higher single-target damage with complimentary skills.

Build Assessment

Pros

+ Affordable, league-start viable.
+ Strong and large area clear.
+ High survivability.
+ Scales simply, being concerned with few stats.
+ Depends on no specific unique items.
+ Levels smoothly with Poisonous Concoction.

Cons

– Requires moderate gear quality before being able to do maximum area clear.
– Pinnacle Bosses and Guardians are slow to die, making pure boss farming strategies unsuitable.
– Needs a mule character or a friend to get the Poisonous Concoction gem. (Method included in guide PoB!)
– Despite very strong defences, it is vulnerable to high damage over time.

Playstyle and Mechanics

Caustic Arrow, unlike most other bow skills, is a ground-targeting skill and deals damage through its secondary effect. This means that when building around it, we’re not concerned about our accuracy, critical strike chance and whether we hit the target with our projectile – but rather about the pool of caustic ground it leaves on impact with the floor. Consequently, we focus on scaling chaos damage and damage over time, which the Occultist ascendancy of the Witch class is especially well suited for.

Occultists are also particularly adept at debuffing enemies, which is one of the defensive layers this build makes use of – by combining curses and a high chance to block attacks and suppress spells with multiple defensive aura buffs, the inherent fragility of a character based on the Intelligence and Dexterity side of the passive tree is nullified. At medium to high investment levels, when most defensive layers are in place and acting together, there’s a high chance you’ll feel like you’re just having a peaceful stroll through what would otherwise be incredibly lethal maps, meaning the build lends itself to a very laid-back playstyle, with the option of ramping up in intensity to more quickly dispatch tougher monsters with a couple more button presses.

Build Progression

With Caustic Arrow depending largely on gem levels and synergies to be an effective skill, progressing through the acts with a much more powerful early-game skill is highly preferred. For this purpose, the Path of Building build provided has detailed a straightforward skill-tree progression for the acts that transitions from Poisonous Concoction to Caustic Arrow at the end of Act 10, using only the passive skill refund points provided by quests (20).

Stage 1 – A Ranger mule character.

The Witch doesn’t get the poisonous concoction gem, so you must create a “mule” – a character created with the express purpose of fetching something for another character – in this case, the Poisonous Concoction gem in Act 1 as a reward from Nessa for reaching the Cavern of Wrath. The guide’s Path of Building includes a skill set and passive tree to make this process as quick as possible. Once you’ve reached this area, teleport back to town, accept the gem as a quest reward and stash it without levelling it, then create your Witch.

If you have a previous character or a friend that is past the Library in Act 3, or playing a Shadow or Ranger alongside you and can give you Poisonous Concoction from Nessa’s quest reward or second shop tab, you may skip this step.

Stage 2 – The Witch character.

Very early on, you’ll level with powerful skills up to where the Ranger character left off if you made a mule and equip Poisonous Concoction after you meet its level 12 requirement.

Stage 3 – Using Poisonous Concoction.

From this point onwards your journey should be incredibly smooth. We’re going all the way through the game’s acts with this powerful levelling skill and grabbing extra utility along the way.

Stage 4 – Switching to Caustic Arrow.

When we’re done with the acts and have a couple of key items ready to go, we switch to Caustic Arrow and never look back.

Path of Building and Passive Skill Tree

All guides on poe-vault.com are provided with a Path of Building, for which you can find a guide here and download from the PoB Community Github.

Click here: for a comprehensive and annotated Path of Building file with item, skill and passive tree progression per act for this build. It also includes different setups for early, midrange, advanced and very advanced progression once in maps.

The Early and Midrange progression setups are focused on being very performant and easy to replicate, while the Advanced and Very Advanced versions of this build are recommended for players with intermediate familiarity with the game’s mechanics and market.

Path Of Building, Skill Trees & Gems

Gearing

This table is a quick-reference resource for what gear to have for the first few stages of progression in maps. For more detailed information on each choice, check the dedicated Gearing section of the guide.

Gear & Flask Choices

Item Slot	Item Name	Rarity
Helmet	A rare item with Life, Resistances and chance to suppress spell damage. When possible, switch to a The Devouring Diadem.	Rare
Amulet	A rare item with Damage over Time Multiplier or +1 to level of All Chaos Skill Gems, but eventually both. Also look for Resistances and Attributes you need.	Rare
Chest	Cloak of Flame is very powerful to start. We upgrade to a rare with chance to suppress spell damage and other defensive stats when possible.	Rare
Gloves	A rare item with Life, Resistances and chance to suppress spell damage.	Rare
Boots	A rare item with Life, increased Movement Speed Resistances and chance to suppress spell damage.	Rare
Belt	A rare Heavy Belt with Strength, to help us meet all our gems and items’ attribute requirements. Also look for Life and Resistances.	Rare
Rings	A Mark of Submission to enable us to easily apply a second curse to our enemies and a rare ring with Life, Resistances and Attributes.	Rare
Weapon	A 6-linked bow with +2 to Level of Socketed Bow Gems and later with +1 to Level of Socketed Gems also. The dexterity requirement should be kept low.	Rare
Quiver	A rare quiver with Damage over Time Multiplier with Attack Skills and increased Damage with Bow Skills. Also look for Life and other DoT stats.	Rare

Levelling

As described in Build Progression above, levelling this character requires that you make a ranger character first, to get the Poisonous Concoction gem, since the Witch does not have access to it as an early quest reward.

The included Path of Building includes item sets and passive trees for the main build as well as for the mule character.

The Acts

After muling Poisonous Concoction or when playing with a friend that can get the gem for you:

Create a Witch character and upon exiting the Twilight Strand, talk to Nessa and pick Rolling Magma as your quest reward.

From here onwards, look for the following gems as quest rewards or sold from Nessa in her second shop tab and try to set them up in the following way when you have the right linked sockets:

1. Main Skill:

• Rolling Magma + Combustion Support + Elemental Proliferation Support

2. Extra Damage:

• Holy Flame Totem + Summon Phantasm Support
• Flame Wall

3. Utility:

• Frostblink + Arcane Surge Support
• Steelskin

4. Auras:

• Vitality
• Clarity

Projectiles from your Rolling Magma and Holy Flame Totem that go through Flame Wall gain its extra damage and apply its debuff to enemies. While fighting bosses, make sure you activate all these skills to maximize your damage.

While progressing through the first 12 levels, look for items with linked sockets:
Green + Green + Blue or Green + Green + Green.

From level 12 onward, Poisonous Concoction should be used instead.

YOUR DAMAGE WILL DEPEND ON YOUR LIFE FLASK TIER.

The skill consumes life flask charges to deal damage, so make sure you carry three of them and upgrade them every time you can. Three of the same tier of life flask sold to an NPC vendor will result in a flask that is one tier higher, making picking up and stashing flasks useful. NPC vendors themselves also sell life flasks relevant to your level for a few scrolls. This is critical to a smooth levelling experience.

Once you switch to concoction, unequip your weapon (it is an unarmed attack) and set your gems up in the following way:

1. Main Skill:

• Poisonous Concoction + Volley Support + Void Manipulation Support or Unbound Ailments Support (G-G-B vs. G-G-G links.)

2. Extra Damage:

• Withering Step

3. Utility:

• Steelskin
• Flame Dash + Arcane Surge Support

4. Auras:

• Vitality
• Clarity

From this point on, look for items with Green + Green + Green + Blue linked sockets and add the support gem you were missing from the ones mentioned above.

In Act 3, once you’ve completed the quest “A Fixture of Fate” in the Library area, purchase and use Defiance Banner and Herald of Agony from the Siosa NPC in the same area.

In Act 3, also purchase a Caustic Arrow gem and keep it socketed somewhere in your gear so that it gains experience and is ready to use later. You can keep it in your alternate weapon set (keybinding set to X by default).

Around the end of Act 5 or start of Act 6, once you have allocated Eldritch Battery and a small mana reservation efficiency node on your passive skill tree, you should stop using Clarity since mana regen will be of very little use to you from that point on. Instead, use Determination or Purity of Elements if most of your resistances are very low (below 40%).

If your Vitality or Clarity auras ever become too high level for your mana pool, you can purchase a level 1 gem from Nessa for very little and level them to an appropriate level until you can sustain the higher reservation costs. To prevent a skill from levelling right-click the “+” instead of left clicking to level it. You can later level it from the bottom of your inventory UI. Be careful not to link support gems to your auras, since their mana cost multiplier will apply to the auras’ reservation cost.

Changing Main Skills

On your way to Act 10 keep an eye out for cheap 6-Linked bows. After Act 10, craft a basic bow by using Orb of Alteration and Orb of Augmentation on it until you hit “+2 to Level of Socketed Bow Gems” or craft a stronger bow with essences as described in the guide section below. Maps and Tips. Then, set your gems up like this:

1. Main Skill:

• Caustic Arrow
• Swift Affliction Support
• Efficacy Support
• Void Manipulation Support
• Vicious Projectiles Support
• Slower Projectiles Support

Keep a Concentrated Effect Support gem in your inventory to swap with Efficacy Support to speed up killing bosses. You can do this in the immunity period you get right after entering a boss arena, before moving. Later, swap Slower Projectiles Support for Empower Support.

2. Extra Damage:

• Vaal Blight
• Infused Channelling Support

• Frenzy
• Greater Multiple Projectiles Support

• Malevolence
• Divine Blessing Support

Use the highest level of Divine Blessing that you have Energy Shield to sustain.

3. Utility:

• Withering Step

• Despair
• Blasphemy Support

• Temporal Chains (socketed in Mark of Submission, applied with Frenzy)
• Blood Rage

• Molten Shell
• Automation Support

• Enduring Cry
• Call to Arms Support

4. Auras:

• Summon Skitterbots
• Determination
• Defiance Banner

Be careful not to accidentally link support gems to your auras, since their mana cost multiplier will apply to the auras’ reservation cost. Make sure you have all the reservation efficiency nodes the guide suggests before attempting to run all auras suggested.

Maps and Tips

• There are no map modifiers this build cannot do. However, if your damage is lacking, you will likely prefer not to run maps with monster chaos resistance or increased monster life.

• If you’re really struggling with resistances after Act 10, make use of the Crafting Bench in your hideout to add stats to your gear. You can also use Purity of Elements instead of Determination, but at this stage the lack of armour will be very noticeable, so try to avoid this situation. Also make sure you’ve allocated all the chance to suppress spell damage passives in the guide tree, including the mastery “Chance to suppress spell damage is lucky.” if you’re not at 100%.

• Spell suppression is very important. A spell that is suppressed deals 50% less damage, and its elemental damage is further mitigated by your elemental resistances, this is a very large factor in your survivability, since without capping it you’ll take sudden spikes of damage from unsuppressed sources. Eventually, when you have enough currency, you’ll be able afford gear with enough spell suppression and gain back quite a few passives on the tree, while remaining capped. These reclaimed passives will translate into more damage.

• Focus on upgrading your bow, gems and jewels, as they are your main source of damage. An early “+3” bow can be crafted with a Deafening or Shrieking Essence of Dread which guarantees the “+2 to Level of Socketed Bow Gems” modifier, by using them on a bow until you hit “+1 to Level of Socketed Gems” – and since the modifier spawned by the essence ignores item level, you can use 6-Linked bows of relatively low item level, such as the Short Bows from The Porcupine Divination Card set. The lowest item level we can use to make this starter bow with Essences is 50. If you have no access to Essences, “+2 to Level of Socketed Bow Gems” requires an item level 64 bow. Remember to get a base with a low Dexterity requirement, so that less attribute rolls are needed on your gear. Level 21 Caustic Arrow requires 159 Dexterity – a bow that requires an amount close to that is optimal.

• Look for relevant cluster jewel bases and regular jewels early on. These can be used within a few levels of finishing the acts and represent a great increase in damage.

Remember, everything provided here is a guide, not gospel. Due to the random nature of items in Path of Exile, your experience is certain to vary from that of other players, especially if you’re inexperienced in the many interlocking systems of the game. For this reason, the ARPG-Vault Discord Server and its experienced players provide channels for the sole purpose of answering questions about every build on this website. Join us for a chat and for any questions you want to ask!