Mad Gasser will only proc auto-Barrier Break at the start of the round. If you recast Barrier they have no way to remove it, almost trivializing the whole fight.
Alternately, you can inherit Null Poison or bring demons immune to ailments like Kinmamon to alleviate pressure off your Barrier caster.
Both Vasuki and Hel have a passive that increases damage done to poisoned enemies, and Vasuki will cast an almighty-AOE when your demons are poisoned. If you used the approach above, you will never run into this scenario, severely reducing the entire team's damage output.
Vasuki will not cast its Ice attack into Alilat + Repel Ice, but Hel will.
With proper buffs and debuffs up, you can mitigate the damage to a very manageable level.
Hecatoncheires is a good choice for this fight, as he reduces AOE damage taken from both Hel and Vasuki, and can also double up as your debuffer / secondary Barrier caster.
Meposumudi used on the first turn will reduce poison infliction chance by 30%, adding Seiran will bring it to 45%. Thus reducing the probability of getting poisoned
Mad Gasser AI may or many not be affected by this (further testing needed but AI may use Mahapoison less often)
Combat stats use the screenshot’s level, STR, MAG and VIT with the base stat formulas. Enemy skill bonuses are not included. HP is the recorded maximum.
Sources
Blob · original encounter screenBlack Ooze · original encounter screen
Wave 2:
Difficulty AEditorial estimate
FEDCBAS
A demanding challenge with barrier removal, Pierce attacks; plan counters and sustained recovery.
Recommended demonsKit-based options · reviewed 14 Oct 2026
Poison enables the bosses’ damage chains. Reapply Barrier after the opening Auto-Barrier Break, or use genuine Poison immunity; cleanse before the damage loop snowballs.
DaisoujouSummon / multifusionAilment and debuff control
His own ailment immunity lets him lead with Cleansing Shout against Poison. This restores the party’s ability to act, removes debuffs and recovers MP without an HP-healing effect.
Merciful Gaze makes her personally Poison-immune and durable, allowing an attacker to remain active while other allies recover. Her support form also removes Spirit Chains.
Setup: This is personal immunity, not party-wide immunity.
With Panel 3, allies in Zenith become ailment-immune. The Zenith package can prevent Poison from enabling the documented boss chains, while Force damage supplies offensive pressure.
Setup: Panel 3; keep the party in Zenith.
Watch out: Without Panel 3 or Zenith, do not claim the team is Poison-immune.
Combat stats use the screenshot’s level, STR, MAG and VIT with the base stat formulas. Enemy skill bonuses are not included. HP is the recorded maximum.
Sources
Hel · original encounter screenVasuki · original encounter screenMad Gasser · original encounter screen
I used Kangaroo Boxer for Position Hack, as the team did not have enough BS.
Kinmamon is immune to ailments and is just here to cast Barrier.
Yoshitsune is the main DPS demon. Mad Gasser has a passive that grants extra evasion though, sometimes it's better to pass than risk a Miss and lost press turns.
Amaterasu is used for buffing and healing. Samarecarm transfer in case you get RNG screwed early on.
Orcus provides a strong debuff in War Cry, AOE reduction and also acts as a secondary Barrier caster.
Save scum until Position Hack triggers and use the turn to set up Barriers and buffs. As long as you keep recasting Barriers and get some occasional Hassou Tobi casts in, you should be able to clear the fight without problems.
Five Elements, Luster Candy, War Cry, and Anti-Ice Pierce can reduce the damage Vasuki and company deal to a manageable level. You'll get Poisoned, but it won't matter.
Quetzalcoatl A can be any DPS, but I picked it because Vasuki and Hel have a Fire weakness.
DaisoujouSummon / multifusion
HirokoLimited collaboration
Ongyo-Ki MSummon-only
Kinmamon
Yoshitsune
Amaterasu
Orcus
Huang Long
Beiji-Weng
Alilat
Seth
Asherah
Quetzalcoatl A