Vashnik the Malignant — Guide to a boss of The Venomous Abyss

Single-phase fight with an enrage at 8 minutes. The room has three fountains at its corners — Blood, Shadow and Flame — and the boss's position relative to them determines everything else.

When energy reaches 100 Vashnik casts Imbibe and drinks from the two nearest fountains. Each Imbibe produces three effects: it deals raid damage while adding a stack of environmental venom that never decays and is the real driver of the enrage; it erupts slimes from the two fountains involved; and it grants the boss an Infusion for each fountain, empowering his abilities of the matching colour and doubling the health of the corresponding slimes. Infusions last a minute and a half, so the boss must be moved from one altar to the next so each Imbibe picks a different pair and no element exceeds two stacks.

The slimes, whatever their colour, head for the Malignant Cavity at the center, and if they reach it they deal huge raid damage with a stacking DoT. Each needs different handling: fire ones are grippable and must be killed staggered because they explode on death, blood ones are CC-immune and must be burned before they arrive, shadow ones carry an absorb that doubles their apparent health.

On Mythic there are also the ground pustules commonly called tumors. If they aren't destroyed they erupt with heavy cumulative damage on the whole raid, and the only tool to remove them is a set of waves generated by a debuff, which the debuffed player has to line up over them.

Anyone who played Kurog Grimtotem will recognise the altar logic.

TL;DR

What to do

Everyone

Always: stop the slimes from reaching the center.
Every Imbibe (Mythic): place the Plague Waves over the tumors. It's the only way to destroy them.
Every Malignant Catalyst: soak the Catalytic Bile splashes.
With Siphoning Infection active: stack tightly in melee.

Tank

Always: kite the boss around the perimeter so each Imbibe draws from a different pair of fountains.
Tank swap on every Dripping Fangs, which grants +200% physical damage taken per stack.

Healer

Always: Toxic Vapor grows with each Imbibe and never decays. Damage is rising attrition.
Shadow infections: refill the Stygian Infection absorbs quickly. It's the only way to close the mechanic.
Every Imbibe: immediate damage spike on the whole raid.

DPS

Always: focus and burst the Clotting Venoms, which are CC-immune.
Always: stagger Burning Venom kills, since their death DoT stacks.
Ranged: someone must watch the whole arena and call out which tumors are still alive.
Dispellers: stagger Exploding Infection dispels, as each removal is a raid explosion.

What can kill you

Ability	When	How to avoid it
Plague Wave	After each Plague Froth	Hitbox is larger than the visual: keep wide
Dripping Fangs	On the current tank	+200% physical damage taken per stack: tank swap
Umbral Ejection	On shadow slime death	Splashes within 3 yards: kill them away from the raid
Stygian Burst	With shadow infection active	Periodic eruption within 6 yards of the infected player
Siphon Blood	With blood infection active	On Mythic Thinned Blood doubles damage on repeatedly drained players
Shadow slime pools	After each shadow Imbibe	They progressively make the area unusable

What wipes the raid

Mistake	When	Consequence
A slime reaches the Cavity	Always	Malignant Burst: huge damage plus a 30-second stacking DoT
Tumors not cleared	After each Imbibe (Mythic)	Malignance: heavy damage plus a stacking 1-minute DoT. Detonation observed at ~60-70 seconds
Too many stacks of one Infusion	Bad kite	Each stack doubles the matching Expulsion damage and gives slimes +50% health
Simultaneous dispels	Flame infections	Multiple Caustic Explosion at once
Burning Venoms killed together	Always	Caustic Surge stacks on Heroic and Mythic
Reaching 8 minutes	Enrage	Accumulated Toxic Vapor makes the raid unmanageable well before

Timeline

Point	What happens
Imbibe (100 energy)	Raid damage, +1 Toxic Vapor stack, two fountains erupt slimes, +1 Infusion per fountain (1:30 duration). Tumors spawn on Mythic
Between Imbibes	Slimes crawl to the center, Plague Froth onto tumors, Malignant Catalyst, Dripping Fangs, Adaptive Infection
Then	Kite the boss to the next pair of altars
~4 minutes	Full cycle across all three fountain pairs
~8 minutes	Enrage

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Detail

The three altars

The room has three fountains at its corners: Blood, Shadow and Flame. At 100 energy Vashnik casts Imbibe and drinks from the two nearest, with three effects:

Heavy raid damage plus a stack of Toxic Vapor, a permanent DoT that grows with each Imbibe.
The two fountains erupt slimes that crawl toward the central Malignant Cavity.
Vashnik gains one Infusion per fountain, lasting 1 minute 30.

Infusion	Effect
Blood Infusion	+100% Hemo Expulsion damage, +50% Clotting Venom health
Shadow Infusion	+100% Gloom Expulsion damage, +50% Shrouded Venom health
Flame Infusion	+100% Conflagrating Expulsion damage, +50% Burning Venom health

Effects stack: two consecutive Imbibes on the same fountain produce slimes with double health.

The rotation

Since Imbibe draws from the two nearest fountains, boss positioning is the mechanic. The boss is moved from one altar to the next so each Imbibe picks a different pair:

Position A → Shadow + Flame
Position B → Flame + Blood     (the Shadow stack expires)
Position C → Blood + Shadow    (the Flame stack expires)

Rotating correctly, you never exceed 2 stacks of any single element. The full cycle observed in PTR testing takes about 4 minutes.

A strategy pushing the same two fountains every time is theoretically possible but unlikely to be worthwhile, given the cost in slime health and Expulsion damage.

The slimes

All of them have one goal: reach the center and explode. If they succeed, Malignant Burst deals devastating damage plus a 30-second DoT, and the effect stacks.

Shrouded Venom (shadow)

Miasmic Coating: an absorb equal to 100% of maximum health, so effectively double the apparent health.
On death, Umbral Ejection: splashes within 3 yards that leave the purple pools. Kill them away from the raid stack and off the boss kite path, or the pools end up where you need to stand.

Clotting Venom (blood)

Sanguineous Fortitude: immune to all CC until destroyed. Must be focused and burned before it reaches the center. With 2 Blood Infusion stacks it has +50% health.
On death, Splitting Clot: splits into smaller slimes, manageable with cleave.

Burning Venom (flame)

They spawn already grouped, so grips aren't for gathering them: they're for repositioning and for staggering the kills, which is the actual point (see Caustic Surge below).
While alive, Burning Presence damages the whole raid every 3 seconds.
On death, Caustic Surge: explosion plus a DoT, stacking on Heroic and Mythic. Kills must be staggered.
Hardened Venom: after 60 seconds they become CC-immune and gain +50% movement speed. Control has an expiry date.

The tumors — Malignant Totem, Mythic

Each Imbibe also generates pulsing pustules on the ground. The journal lists them under two different names, Malignant Totem in the Imbibe section and Malignant Tumor in the Plague Wave description, and the description is incomplete.

If not destroyed they cast Malignance: high immediate raid damage plus a 1-minute DoT, and the effect stacks. In PTR testing autonomous detonation was observed after roughly 60-70 seconds and is the most frequent cause of wipes. That figure is an estimate from wipe footage, not a journal value.

They can only be destroyed with Plague Waves.

Plague Froth debuffs several players: while active it damages within 4.5 yards, so spread out, and on expiry it erupts into four waves along the cardinal directions from the player.

On Normal and Heroic the waves are just an obstacle. On Mythic they are the tool that removes tumors: the debuffed player positions so that at least one line passes over a pustule. The wave hitbox is larger than the visual, so alignments that look like near-misses still work.

Tumors often spawn at the far end of the room, away from wherever the raid is standing. Someone must watch the whole arena and call out which pustules are still alive, and a clean UI helps.

Other abilities

Malignant Catalyst (Heroic/Mythic) — an orb of venom above the Cavity explodes, damaging the raid and launching Catalytic Bile splashes. Each splash must be soaked within 6 yards; if one hits no player, the damage goes to the whole raid instead.

Dripping Fangs — tank bite: huge physical damage, a 32-second DoT and +200% physical damage taken, cumulative. Tank swap on every application.

Adaptive Infection — infects players with the venom type matching the active Infusions. Changing altars changes the infection package.

Exploding Infection, flame — fire DoT. On removal the player erupts into Caustic Explosion on the raid. On Mythic it gains a stack every 1.5 seconds until dispelled. Debuffed players step out and dispels must be staggered.
Stygian Infection, shadow — periodic damage plus a healing absorb. While it lasts the player casts Stygian Burst, an eruption within 6 yards. Healers must refill the absorb quickly.
Siphoning Infection, blood — the marked player receives a huge healing absorb and healing received is reduced by 100%. The only way out is Siphon Blood, which drains life from nearby allies, damaging them and healing the infected player in proportion to how many allies are hit.

(?) For Siphoning Infection, barring surprises in live tuning, coordinating voluntary rotations isn't worth it: with Thinned Blood on Mythic, the more a player is drained the more damage they take, making rotations unmanageable. Stack tightly in melee and let the infected player fill up while the drain spreads. Ranged therefore spend much of the fight in melee.