Mastering the Underroot Dungeon - A Complete Guide

If you‘re looking to seriously upgrade your hero and take on Diablo IV‘s toughest challenges, conquering the notorious Underroot dungeon is a must. This sprawling subterranean labyrinth is packed with vile monsters and elite bosses guarding some of the game‘s best loot.

But surviving the Underroot‘s endless hazards and twisted passageways takes proper preparation. You‘ll need the right strategies, skills, and gear to fully explore the Underroot‘s three deadly levels and defeat its overlords.

In this complete guide, I‘ll share everything you need to know to traverse the Underroot, beat its bosses, and claim your just rewards. You‘ll learn tips from my own hard-won experience in the Underroot trenches. So grab your sword and follow me on a journey to the dark heart of Scosglen!

What Exactly is the Underroot?

Before we dive in, let‘s quickly cover what exactly the Underroot location is for those new to Diablo IV. Deep beneath the city of Scosglen lies a vast subterranean complex once used by mages for magical experiments away from prying eyes.

Now overrun by demons, the sprawling Underroot dungeon is divided into three distinct sections across multiple levels. It‘s packed with elite enemies, deadly environmental hazards, and unique bosses guarding coveted treasures.

While entirely optional, conquering the Underroot offers some of Diablo‘s best loot opportunities. Surviving its labyrinth tests your skill and rewards persistence. But the dangers here far exceed most surface regions. Only head underground when you‘re ready for a true challenge!

Where to Find the Underroot Entrance

The first step is actually locating the Underroot‘s hidden entrance. You‘ll first need to complete the "Trouble Underfoot" questline given by Halnyx Tenderhoof in Scosglen. After dispatching the bosses lurking below for him, the Underroot will remain open.

The entrance itself lies in southern Scosglen just southeast of the central marketplace. Look for a conspicuous stairwell leading down marked by a hanging sign.

If you have trouble finding it, open your area map and look for the dungeon icon. With the entrance revealed, we can begin our descent!

Level 1 – Surviving the Fungal Forest

Your first steps into the Underroot lead you into a humid fungal forest. The air hangs heavy with spores here as massive mushrooms and alien plants block your path. Tread carefully, as many of the fungi conceal deadly surprises:

Poison Puffers unleash toxic clouds that inflict Nature damage over time. Their spores spread to nearby foes, so don‘t cluster together.
Spore Bursters live up to their name, exploding violently when slain. Lure these walking bombs away from your allies before attacking.
Carnivorous Stalks are stationary tentacles that grab players, dealing crush damage. Cut them down quickly to avoid getting snared.
Overgrown Custodians are elite champion enemies shielded by a painful thorn aura. Focus fire to take them down before their damage stacks up.

Carving through the Underroot‘s overgrown entrance tests your crowd control abilities. Use snares, stuns and slows to isolate dangerous targets and limit how many foes you face at once. Stay mobile and be ready to retreat if you get overwhelmed.

Thallak the Contaminated

Beyond the fungal thickets, you‘ll eventually reach a sunken grotto guarded by the first Underroot boss, Thallak the Contaminated. This insectoid horror summons swarms of virulent scarabs and pelts you with poisonous attacks:

Thallak unleashes swirling poison nova blasts, leaving toxic pools on the ground. Don‘t stand still or get cornered.
He calls down locust swarms that chase you and explode on contact. Keep moving and use healing over time abilities to counteract their damage.
At 50% health, Thallak goes into a frenzy. His attacks grow faster and deadlier through the remainder of the fight. Finish him quickly once enraged.
Thallak‘s swarmbringer staff drops on defeat. This ceremonial weapon boosts minion damage by 15%.

Overall Thallak serves as a skill check for your Underroot journey. If you can dodge his attacks while managing add swarms, you‘re ready to descend further.

Level 2 – Surviving the Alchemical Labs

Passing Thallak‘s chamber, you‘ll enter the Underroot‘s second segment – a network of abandoned alchemical labs still brimming with volatile reagents. Tread lightly as pretty much everything in here can kill you:

Fungalmancers unleash fungal attacks like entangling roots and spore barrage volleys. Interupt their spells to stop the damage.
Lab Guardians are magic-resistant elite enemies. Use crowd control and save your hardest hitting abilities to punch through their defenses.
Alchemic Oozes leave pools of sizzling acid on the ground when they die. Don‘t get cornered in the burning goo.
Gas Canisters explode when struck, igniting anything nearby. Either avoid or carefully snipe them from a distance.

Much of the lab area involves managing environmental hazards as much as the enemies themselves. Advance cautiously and don‘t be afraid to pull back and reset a room if things get too hot.

Vylla, Voice of Zavain

The mystic Vylla awaits at the end of the alchemical labs. A devoted follower of the eldritch being Zavain, Vylla wields an arsenal of elemental and psychic attacks:

Vylla teleports frequently, making targeting difficult. Predict where she‘ll blink to next.
Lightning orbs fire from her staff, leaving patches of charged ground. Keep moving to avoid the chaining damage.
At low health, Vylla surrounds herself in an ice barrier, freezing nearby players while enhancing her attacks. Back off if you get trapped in ice.
Vylla‘s robes provide a 15% buff to elemental skill damage when looted, great for caster builds.

With care, patience, and quick reflexes, you can overcome Vylla‘s mystical onslaught. But your trials in the Underroot have only just begun…

Level 3 – Braving the Rift

The final Underroot segment takes you into the source of Scosglen‘s woes – a spatial rift leaking cosmic horrors into the city. Here you‘ll fight on platforms precariously suspended over a bottomless void:

Voidmasons are elite enemies that summon invisible etheral walls to block your path. Carry movement skills to bypass obstacles.
Riftwalkers teleport around while bombarding you with temporal anomaly attacks that slow time. Kite and damage them down.
Collapsing platforms have a short timer before falling into the void. Keep moving and stay off of platforms that start cracking apart.

This area tests both your navigation skills and ability to counter ranged attackers. Stick and move rapidly to deal with threats before getting pinned down.

Garosh, Maw of the Void

The spatial rift‘s anchor point is the monstrosity Garosh, Maw of the Void. Garosh switches between melee attacks and casting devastating laser and portal abilities:

Garosh claws at nearby enemies while reflecting back a percentage of melee damage dealt. Ranged attacks are safer.
He fires piercing lasers that knock you back and drain life. Sidestep the beams.
Void portals summon demonic adds to aid Garosh. AoE attacks help thin their numbers.
Garosh‘s looted rift guard chest piece reduces crowd control durations by 20%.

Staying mobile while handling adds and avoiding Garosh‘s planet-cracking lasers are the keys to victory here. Defeating Garosh seals the rift for good, cutting off the flow of void creatures plaguing Scosglen.

Underroot Boss Loot Breakdown

So you‘ve conquered the Underroot‘s horrors and toppled its overlords. Now it‘s time to tally up the loot! Here‘s a quick breakdown of what each boss drops:

Boss	Loot Drops
Thallak	Swamp Stomper boots (15% movement speed in swamps)
Vylla	Fungalmancy wand (15% poison & elemental damage)
Garosh	Rift Guard chest armor (20% reduced crowd control duration)
All Underroot Bosses	Crafting mats like Defiled Bone, Eldritch Embers, Enchanted Sinew, and Corroded Crystal for legendary sets
All Underroot Bosses	Random legendary weapons, rings, amulets, and other equipment

While their signature loot is great for specific builds, all the bosses have a chance to drop other top-tier gear too. The more of the Underroot you clear, the more rolls you get at that sweet sweet purple equipment.

Claiming the Aspect of the Expectant

Completing the entire Underroot (all bosses and bonus objectives defeated) rewards you with the Aspect of the Expectant item. This unique artifact causes your Basic Attacks to increase all damage dealt by your Core Skills by 5%, stacking up to 30%.

This is an insane damage buff for any hero relying on spammable Core Skill attacks. I can‘t recommend grabbing the Aspect enough – it will noticeably amplify your power across the board.

To claim your Aspect, speak to the surviving Scosglen townspeople after finishing the Underroot. They will gratefully award you the relic for liberating their city from the dungeon‘s foul influence. Equip it to immediately feel the difference in combat.

Optimizing Your Build for the Underroot

Now let‘s discuss how to best optimize your hero build and gear to survive the Underroot‘s deadly trials. Here are my top tips:

Prioritize poison and elemental resistances

Much of the Underroot‘s damage comes from poison and elemental attacks. Stack gear and passive skills that enhance these resistances. Antidotes and vitality are clutch as well.

Pack area damage for add clearing

From fungus swarms to void portals, the Underroot throws lots of minions at you. Cleave, multi-shot, chain lightning – bring AoE damage to thin the herd.

Take mobility and CC options

Kiting, teleports, stuns, slows – tools that help control the battlefield will carry you far here. Don‘t get trapped or overwhelmed.

Lean into ranged damage vs. bosses

Against Thallak, Vylla, and Garosh, melee is risky due to explosions, teleporting, and knockback attacks. Ranged skills let you stay safe and keep dishing damage.

Sustain and leech offset decaying damage

Poison, acid, and void zones mean you‘ll take incremental damage. Mitigate this with hearty sustain via life leech, regeneration, healing skills, etc.

There are far more effective builds and gearing strategies than I can list here. But in general, prioritizing survival, mobility, AoE damage, and ranged attacks will take you far in the Underroot. Play smart, and you‘ll reap the rewards.

Conquering the Underroot – Closing Thoughts

The Underroot remains one of Diablo IV‘s greatest challenges – a true test of skill with some of the best loot as the prize. I hope my guide has prepared you to brave Scosglen‘s deadly depths and emerge in triumph.

Here are my final tips before you descend:

Don‘t attempt it underlevelled or undergeared – around level 53+ is recommended.
Explore carefully and pull back often. Don‘t let yourself get swarmed.
Study and recognize each enemy‘s attacks to dodge effectively.
Keep your mobility and crowd control skills handy.
Maintain your antidotes, potions and health management.
For bosses, stay on the move and watch their telegraphs.
Play patiently and don‘t get greedy! Surviving comes first.

Follow these steps and the Underroot‘s villainy will be no match for your might. Stay awhile and listen, hero…destiny awaits underground. I‘ll see you in the depths!