The Eris Protocol: Master the Underworld

At a glance

Part 1: First steps and permanent progression

First runs:

• Learning Enemy Patterns: Get a feel for how enemies move and attack in each biome. Don't be afraid to just dodge and observe in new encounters.
• Gathering Key Resources: Focus on collecting Chthonic Keys, Nectar, and Darkness. These are essential for permanent progression in the House of Hades.

What you can and cannot undo

Most choices can be redone. These cannot.

Easy to undo

• Mirror of Night Talents: Don't worry about mistakes here. You can reset any individual talent choice at the cost of one Chthonic Key, allowing you to experiment freely.

Essential items: your first Nectar gifts

Give your first Nectar to these characters:

Part 2: Building your permanent power base

Spend resources between runs:

A. The House Contractor: foundational upgrades

This shady figure lets you purchase upgrades for the Underworld. Prioritize these with your Gemstones:

• Fated List of Minor Prophecies: Your first purchase. It provides goals that award large amounts of essential resources.
• Fountain Chambers (All Biomes): Guaranteed healing rooms are invaluable, especially at high difficulty. Purchase Tartarus first, then Asphodel, then Elysium.
• Regional Keepsake Collection: This is the absolute cornerstone of this strategy. It allows you to switch keepsakes between biomes, which is how you will force this build into existence.
• Rod of Fishing: A minor but useful upgrade that lets you fish for extra resources in designated spots.
• Boons - Rare Crop / Epic Crop: (Later-game purchases) These passively increase the rarity of boons you encounter, further optimizing your runs.

B. The Mirror of Night: your core talents

This is where you spend your Darkness to gain permanent power. Use your Keys to buy all 24 talents. Here are the recommended choices for this build, roughly in order of priority for a new player:

Part 4: Mastering the build, combat and contingencies

The Eris buff and combat loop

The Aspect of Eris's power comes from its unique buff:

• Buff Activation: Fire your Special at a nearby wall or directly at your feet.
• Absorb: Immediately dash into the explosion's radius to absorb the Eris buff, granting a {{fact:buffBonus}} global damage bonus for {{eris:1:duration}}.
• Annihilate: While buffed, hold down the attack button and begin aggressively dash-striking into and through enemies. Your Lightning Strike Attack, Tidal Dash, and Heartbreak Flourish Special will rapidly apply curses and deal massive damage.
• Advanced Technique: To maintain 100% buff uptime, weave your Special into your Rail's reload animation; firing the Special will cancel the reload, letting you keep up the pressure.

Daedalus Hammer priority

Hammers modify your weapon significantly. Prioritize these for the Eris Rail:

• Cluster Bomb: The single strongest upgrade. Modifies your Special to fire 5 bombs, making it incredibly easy to absorb the Eris buff consistently and clear rooms.
• Rocket Bomb: Transforms your Special into a fast, direct-fire rocket. The combination of Cluster Bomb + Rocket Bomb is the build's strongest form, turning your Special into a major damage source.
• Triple Bomb: A solid alternative that allows the Special to be fired 3 times in rapid succession, still excellent for Eris buff uptime.

Strategic pivots when RNG resists

Even with keepsake forcing, RNG can sometimes be stubborn. Here's how to adapt:

• If Sea Storm Refuses to Appear: Pivot to a Pure Zeus build. Abandon the hunt for Poseidon's Duo Boon and focus entirely on stacking Zeus's secondary boons (Double Strike, Splitting Bolt, Stormy Judgment) to maximize raw lightning damage.
• If You Cannot Find a Good Hammer: Re-classify your Special as a pure utility tool. Its only purpose now is to be fired at your feet every {{eris:1:duration}} to activate the Eris buff and apply the Weak curse. Focus on your primary attack damage and Dash instead.

Part 5: Optimizing your build and beyond

Once you have the core build down, these points help you push its power even further.

1. Optimizing your "filler" god slots

The core guide correctly locks in Zeus, Poseidon, and Aphrodite. However, you will inevitably encounter other gods. Planning for them can lead to significant gains.

The case for Artemis, the best "fourth god"

Artemis is arguably the best "fourth god" for this build. Her boons provide a multiplicative damage increase, which is exactly what you want.

• Pressure Points: A chance to deal critical damage on any hit. Since this build hits so many times per second with Zeus's lightning, this adds a substantial, independent layer of damage.
• Support Fire: Adds a seeking arrow every time you Attack, Dash, or use your Special. Each arrow is another instance of damage that can trigger the effects of Sea Storm.
• Legendary Boon - Fully Loaded: Getting +2 Cast stones from Artemis is a direct upgrade to the Infernal Soul you already have, giving you more ammo for Boiling Blood.
• How to Integrate: If you see an Artemis door in Elysium or Styx and your core build is already online, taking it is almost always the correct choice.

2. Choosing the right Call (God Gauge)

The guide doesn't specify a Call, which is a major source of damage and utility.

• Best Defensive/Utility Call: Aphrodite's Aid. The Charm effect is one of the strongest defensive tools in the game. A max-gauge call will neutralize threatening foes or bosses for a long duration, allowing you to deal uninterrupted damage safely.
• Best Offensive Call: Zeus's Aid. Fits the build perfectly. It charges quickly and adds a large amount of lightning damage, working with your other Zeus boons like Static Discharge and Double Strike.

3. The Eris Aspect investment itself, the biggest improvement

This is the most important point for maximizing the build's power. Investing Titan Blood into the Aspect of Eris is the single most important upgrade you can make for this build.

• What it does: Each level of investment increases the duration of the {{fact:buffBonus}} damage buff you get from absorbing your Special's blast.
• The Gain: At Level 1, the buff lasts {{eris:1:duration}}. At max Level {{eris:max}}, it lasts {{eris:max:duration}}.
• Why it Matters: A longer buff means you refresh it less often. This results in a massive increase in "up-time" where you are just holding down the attack button and dashing. It's a colossal boost to both your real-world DPS and your mental focus. This is the highest priority for your Titan Blood and has no diminishing returns until it is maxed out.

4. Advanced companion strategy

Companion Battie is excellent for front-loading damage. However, for higher Heat levels, an alternative can be even better.

• Companion Shady (Skelly): Summons a distraction that draws enemy fire. This is invaluable in chaotic rooms, especially the fight against Theseus and Asterius or the final boss. "Shady" creates breathing room for you to safely reload and re-apply your Eris buff. It's a strategic choice that trades burst damage for control and safety.

Part 6: The endgame, the Pact of Punishment and resource farming

After your first successful escape, you will gain access to the Pact of Punishment. This allows you to add "Heat" to your runs to earn new rewards from bosses.

Scaling the Heat safely

• "Free" Heat: Start by adding ranks to Forced Overtime (increases enemy speed/attack rate) and Damage Control (enemies have temporary armor). This build's high mobility and fire rate make these pacts relatively easy to handle.
• Calculated Risks: Extreme Measures (up to Rank 3, which reworks boss fights) and Underworld Customs (cannot acquire certain boon types again after selling/trading) are safe sources of Heat for this build once you're comfortable. Avoid Extreme Measures 4 (the final boss) until you are very confident.
• Nuanced Pact Choices:
  • Tight Deadline: This build is incredibly fast. Once you're comfortable with boss fights, you can add all three ranks of Tight Deadline for 6 "free" Heat with almost no change in difficulty.
  • Benefits Oversight: Level 1 of this pact (foes gain one pip of armor) is trivialized by the high-frequency chain lightning hits, which strip armor almost instantly.
  • Approval Process: This pact, which limits your boon choices, should be one of the very last Pacts you ever take. It directly conflicts with the guide's core philosophy of forcing specific boons into existence and can easily break a run.

Resource farming guide

Titan Blood, for upgrading weapon Aspects

• Primary Method: Defeating the first and last boss on a new Heat level with each weapon.
• Other Sources: First-time clears with each weapon, completing Prophecies, buying from the Wretched Broker (for {{fact:brokerAmbrosia}} Ambrosia) or Styx Shop (for {{fact:styxTitanBloodObols}} Obols), and fishing in the final boss area.
• Irreversible Note: Spending Titan Blood is a major time investment. Use this guide to invest in the Aspect of Eris first before spending it on other aspects you may not enjoy.

Diamonds, for House Contractor upgrades

• Primary Method: Defeating the Bone Hydra (second boss) on a new Heat level with each weapon.
• Other Sources: First-time clears, completing Prophecies, buying from the Broker or Styx Shop (for {{fact:styxDiamondObols}} Obols), and fishing on the surface.
• Irreversible Note: Prioritize functional upgrades (like the Regional Keepsake Collection) from the House Contractor. Cosmetic items are a permanent resource sink with no gameplay benefit.

Ambrosia, for relationships and companions

• Primary Method: Defeating Theseus and Asterius (third boss) on a new Heat level with each weapon.
• Other Sources: First-time clears and completing the majority of the Fated List of Minor Prophecies.
• Irreversible Note: Do not trade Ambrosia for Titan Blood at the Wretched Broker unless you have a massive surplus. Ambrosia is rarer and more important for late-game story progression.

General farming tips

• Dark Thirst: Always use the weapon with the purple glow in the Arsenal Room for a 20% bonus to Darkness and Gemstones.
• Boons: Look for Poseidon's "Ocean's Bounty" and Chaos boons that increase your resource gains.
• Chambers: Prioritize chambers with Infernal Troves that offer Gemstones or Darkness.
• Fishing: If you have the Rod of Fishing from the House Contractor, always check for fishing spots when entering a room; they provide valuable bonus resources.

Part 7: Advanced mastery, nuance and execution

For players looking to push this build to its absolute limit, these points focus on in-run mastery and subtle decision-making that can provide marginal yet consistent gains.

1. Chamber pathing beyond boons

• Resource Opportunity Cost: Evaluate the opportunity cost of each door. Sometimes, taking a Darkness door or a Gemstone trove, especially in Tartarus, if it leads to a shop where you can buy a Pom, a key core boon, or a helpful Charon's Well item, is more valuable than an early god door that doesn't immediately fit the build. This requires deeper knowledge of shop inventories and resource needs.
• Avoiding "Dead Ends": Learn to recognize when a particular god door or hammer room isn't going to help the current state of your build. Consciously choose a less optimal (but not detrimental) path to preserve re-rolls or ensure access to a needed item later.
• Charon's Wells: These are often overlooked. Knowing which well upgrades are beneficial for the build at specific stages (e.g., increased Special damage for Eris buff consistency, or extra Obols to guarantee a shop purchase) can be a subtle but impactful gain.

2. Shop management and Charon's Obols

• Strategic Spending: Beyond just buying core boons, knowing when to buy a Pom (and for which boon), a Centaur Heart (Max HP), or a specific well item, versus saving for a potential mid-biome shop or even a Styx shop item (like Titan Blood or Diamonds), is a critical skill. Use Deep Pockets well.
• Charon's Trial: For expert players, intentionally losing to Charon in his shop (after securing all needed purchases) grants a valuable 300 Obols and a free item. This is a high-risk, high-reward maneuver for those confident in their combat abilities.

3. Enemy behavior

• Privileged Status Uptime: While the guide emphasizes applying two curses, a truly optimized player will have near 100% uptime on Privileged Status against every single enemy. This means quick re-application of Jolted (from Attack) and Weak (from Special/Dash) even in chaotic scenarios.
• Backstab Positioning: Shadow Presence is a core Mirror talent. An expert player will constantly be positioning themselves for backstabs, especially against armored foes or bosses, to maximize this "free" damage. The Rail's dash-strike makes this relatively easy to execute.
• Boss Phase Knowledge: Knowing exactly when bosses become vulnerable, when to hold your Call, and when to spend all available damage is key to faster clears and less damage taken. For example, using Aphrodite's Call to charm Theseus precisely when he's vulnerable after Asterius is down, or saving Zeus's Aid for a specific boss phase.

4. Death Defiance management and recovery

• Avoiding Unnecessary Deaths: This sounds obvious, but a master player conserves Death Defiances. This isn't just about not getting hit; it's about making smart decisions regarding risk-taking and when to disengage or use defensive options.
• Death Defiance Recovery: Prioritizing Death Defiance recovery items from shops, Charon's Wells, or Patroclus, especially before a difficult boss, is a significant "gain" in terms of run consistency and safety at higher Heat levels.

5. Using your Cast

• While the focus is on the Attack, remember your Cast. With Infernal Soul and Boiling Blood, a well-placed Cast can significantly burst down a single, tough enemy or provide needed damage against a boss if your main Attack is temporarily inconvenient due to enemy positioning or invulnerability frames.

Part 8: Advanced mastery, optimal micro-decisions

These final points represent the highly refined decision-making that can further enhance runs for the most experienced players, recognizing subtle interactions and situational advantages.

1. God pool sizes and Duo Boon chances

• While you force Zeus, Poseidon, and Aphrodite, understanding that having fewer gods in your active pool increases the chances of getting specific boons from the gods you do have can influence minor early decisions. For instance, if you get a random, non-critical god offered early in Tartarus (e.g., Demeter or Ares via a Trial of the Gods door you don't need), sometimes skipping them entirely (if it doesn't give you something vital) can subtly increase the pool concentration for your desired gods later. This is incredibly minor but technically a "gain."
• Similarly, being aware that Duo Boon chances increase after you have two compatible boons from the prerequisite gods is key. The guide already covers this for Sea Storm, but extending that mental model to other opportunistic Duos (like Smoldering Air or Low Tolerance, if they happen to appear) is part of mastery.

2. Keepsake cycling: proactive or reactive

• The guide masterfully uses keepsake cycling. A further refinement is the timing and reasoning behind the Pom Blossom vs. Evergreen Acorn swap in Elysium/Styx.
  • Proactive Pom Blossom: If your core boons are already strongly established and you're confident in upcoming encounters, putting on Pom Blossom immediately after Asphodel can start leveling boons sooner, providing a compounding benefit over more rooms.
  • Reactive Evergreen Acorn: If you took significant damage in Asphodel, or you know a particularly tough Elite room or mini-boss is coming up, switching to Acorn first provides immediate defensive benefit. It's about adapting to your current HP and the known layout of the biome.

3. Other useful boons from your core gods

• Beyond the "must-haves" and "high priority," recognizing the utility of other boons from your core gods can refine your pick order if the ideal boons aren't offered.
  • Zeus: While Lightning Strike and Static Discharge are paramount, boons like Thunder Flourish (Special) or Heaven's Vengeance (Revenge) can still add significant Jolted procs and overall lightning damage if the main Attack boon is already strong. They contribute to Privileged Status uptime from additional sources.
  • Poseidon: Besides Tidal Dash, Typhoon Surge (Dash damage from Wall Slam) or Razor Shoals (Rupture status) can sometimes provide an additional status curse for Privileged Status if Aphrodite is elusive, or simply add more. Again, these are situational.

4. Shop before boon

• In rare scenarios, if you are very low on Obols but desperate for a specific Charon shop item (e.g., a Pom for Sea Storm, or a Death Defiance for an upcoming boss), it might be worth taking a path that guarantees a shop before a boon room, even if the boon room has a desired god. This sacrifices a chance at a boon for a guaranteed purchase. This requires intimate knowledge of biome layouts and shop spawn rates.