Hell's Park Underside

Hell's Park Underside is a mode where you fight bosses that have customizable difficulty levels.

Overview

Hell's Park Underside re-uses the area names of the original Hell's Park, but it has only 1 boss fight (consisting of 4 enemies) per area. Each boss can have their difficulty level customized, starting at level 1 and going up to an unknown maximum.

Clearing a stage for the first time grants gold and silver Friendship Badges, which can be exchanged for rewards. These first-clear rewards are reset every month.

Difficulty levels

Before challenging a stage, its difficulty level can be selected. Higher difficulties will increase enemy stats, add skills to the enemy, and add team-building restrictions.

• Enemies start with 3 skills. They gain their 4th at level 3, their 5th at level 6, and their 6th at level 9.
• After level 9, the only thing that changes is stats.

When a stage is cleared, the player receives the reward for that level, as well as the rewards for all levels below it. These rewards reset monthly.

Initially, only 10 difficulty levels are available for each stage. Clearing level 10 on a stage unlocks levels 11-20 for that stage, clearing level 20 unlocks levels 21-30, and so on.

• The maximum possible level isn't currently known, but someone has reached level 240. It's probably safe to assume that the levels are effectively infinite.

Level	Gold	Silver
1	50	50
2	50	50
3	50	200
4	20	200
5	20	200
6	10	300
7	10	300
8	10	300
9	5	400
10	5	400

After the first 10 levels, each level no longer gives gold badges. Instead, each level gives a standardized amount of silver badges, depending on the level range.

Level	Silver per level
11-20	300
21-100	50
101+	10

Rules

All battles in Hell's Park Underside have a general set of restrictions in place:

• You cannot pierce attributes (for example, Fire Pierce effects will not work). Enemies can still pierce, though!
• Attribute affinity down does not work.
• Anti-pierce effects do not work.
• Effects that increase your Press Turns or decrease the enemy's Press Turns do not work.
• Effects that prevent spending a Press Turn (such as Chief God's Rage) do not work.
• Remnants and Critical Hits will not use half a Press Turn (however, if an attack with those qualities also hits a weakness, then you do use half a Press Turn).
• Damage reduction and reverse damage reduction do not work.
• Dx2 Skills (from Liberators) do not work.

Additionally, each area will impose their own restrictions on the demons you can bring, depending on the difficulty level selected.

However, you are allowed to use items for reviving, healing, etc!

You are also allowed to use your Devil Connector.

Special Skills

Some skills have special effects that only activate in Hell's Park Underside. Some of these skills are further restricted to only a specific area of HPU, and/or are exclusive to certain demons.

Type	Name	Specific area?	Exclusive?	Notes
Passive	Pixie (Underside)	-	Pixie	Available through silver badges in Jan 2025.
Passive	Illuyanka (Underside)	Grave Area only	Illuyanka	Available through silver badges in Feb 2025. A Red Illuyanka with this skill was distributed on Jan 20, 2025.
Passive	Koumokuten (Underside)	Kawara Area only	Koumokuten	Available through silver badges in Mar 2025.
Passive	Fortunate park visitor	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Phys	Struggle Slash (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Fire	Trisagion (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Fire	Fire Slash (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Ice	Ice Age (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Ice	Ice Slash (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Light	Thunderclap (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Light	White Slash (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)

Rewards

Friendship Badge shop

Gold badges

Exchange Lineup	Gold badge cost	Cap
Lost Name	600	1
Lost Name Spirit × 10 (1st set)	100	10
Lost Name Spirit × 10 (2nd set)	150	20
Lost Name Spirit × 10 (3rd set)	200	30
Transcend Stone for Lost Name × 1 (1st set)	100	94
Transcend Stone for Lost Name × 1 (2nd set)	200	88

Notes:

• Initially only Lost Name is available, but after buying him, the spirit and transcend options are unlocked.
• Each set of spirits is unlocked after the previous set is exhausted. The same concept applies to the transcend stones.
  • Panel 1 costs 1,000 badges, Panel 2 costs 3,000 badges, and Panel 3 costs 6,000 badges, totaling 10,000 badges to get all 3 panels.
  • Gold badge income is currently 690 per month, assuming you clear level 10 of each area.

Silver badges

Exchange Lineup	Silver badge cost	Cap
Hell Genome Cube × 1	1,000	No Cap
Pixie (Underside) Genome	3,000	1
Illuyanka (Underside) Genome	3,000	1 / Month
Koumokuten (Underside) Genome	3,000	1 / Month
Sword of Kusanagi 5★	100	20 / Month
Yata Mirror 5★	500	5 / Month
Yasaka Magatama 5★	200	5 / Month
Kasane Magatama	3,000	2 / Month
Aether Crystal	1,500	1 / Month
Skip Ticket (Sin) x20	3,000	1 / Month
Essence of Sin x160	2,000	2 / Month
Mitama Extract St x10	300	5 / Month
Mitama Extract Ma x10	300	5 / Month
Mitama Extract Vi x10	300	5 / Month
Mitama Extract Ag x10	300	5 / Month
Mitama Extract Lu x10	300	5 / Month
Blank Genome	1,500	2 / Month
6★ Brand Cube	500	10 / Month

The Hell Genome Cube gives a random skill genome from a very large pool. A few of the skills are rare and exclusive:

Genome	Notes
Fortunate park visitor	Rare, exclusive
Struggle Slash (Underside)	Rare, exclusive
Trisagion (Underside)	Rare, exclusive
Fire Slash (Underside)	Rare, exclusive
Ice Age (Underside)	Rare, exclusive
Ice Slash (Underside)	Rare, exclusive
Thunderclap (Underside)	Rare, exclusive
White Slash (Underside)	Rare, exclusive

Rotation history

3 areas are available per month, with the available areas and their challenge conditions rotating each month. The demon-specific Underside skill in the shop also rotates each month.

Month	Challenge type			Shop genome
	Fusibles	Race	Low-grade
Jan 2025	Spike Hell	Kawara	Grave	Pixie (Underside)
Feb 2025	Spike Hell	Kawara	Grave	Illuyanka (Underside)
Mar 2025	Kawara	Spike Hell	Sanzu River	Koumokuten (Underside)

Guide

Kawara Area (weak to Phys)

Overview

Feng Huang	Hresvelgr	Tsukuyomi	Feng Huang

Resistances
Feng Huang	Wk	Nu	Wk	-	-	-	-
Hresvelgr	Wk	Wk	Dr	-	Nu	-	-
Tsukuyomi	Wk	Nu	Nu	Rs	Rs	-	-
Feng Huang	Wk	Nu	Wk	-	-	-	-
Battle Speed			10,000

Skills on multiple demons:

Skills on Feng Huangs only:

Skills on Hresvelgr only:

Skills on Tsukuyomi only:

Explanation

• The enemy will start the battle by casting Repel Physical. Tsukuyomi will cast it again when the enemy turn starts, and Hresvelgr will cast it if anyone on your team dies.
• Hellbound: Ice will apply 5 stacks of Spirit Chains of Suppression to you.
• If you fail to kill the adds by the start of their second turn, they will hit you with a bulwark-piercing, 100%-crit enrage AoE. Hresvelgr will do one too, if he isn't dead by his third turn.

Fusibles challenge

Team restrictions:

Difficulty	Restriction
Lv 3-5	3 or more demons must be fusible*.
Lv 6-8	4 or more demons must be fusible.
Lv 9+	All 5 demons must be fusible.
Lv 6+	1 or more demons must be grade 79 (4★ base) or lower.
Lv 9+	1 or more demons must be Clear.

Notes regarding fusibles:

• Multi-fusions count.
  • Beelzebub☆ counts, despite needing a gacha-exclusive material to make him.
  • The following limited-time multi-fusions count: Masakado A, Alice A, Asura. All other limited-time multi-fusions do not count.
• Pixie and Slime count, even though you cannot fuse them.

General strategy:

• For level 9+, you need to run a team of all fusibles, with a focus on Phys damage. One of your demons must also be Clear, and one must be grade 79 or lower (meaning 4★ or lower base rarity).
• Transfer Tetra Break to your fastest unit, and have them cast it when the fight starts to remove the enemy's shield.
• After the shield is down, spam Phys attacks to hit the enemy's weaknesses. Try to ensure Tsukuyomi dies quickly, so he can't re-cast the shield.
• If you have a Koumokuten with the skill Koumokuten (Underside), bring that. He provides a 20% Phys damage and 50% accuracy aura to the team, and when a team member uses Tetra Break, he follows up with DEF and EVAC debuffs, plus a Phys hit directed at the boss. He's also a good choice to satisfy the 4★ and Clear requirements.

Race challenge

Team restrictions:

Difficulty	Restriction
Lv 3-5	All 5 demons must be of the races Genma, Kishin, Night, Drake, or Tyrant.
Lv 6-8	All 5 demons must be of the races Genma, Kishin, Night, or Drake.
Lv 9+	All 5 demons must be of the races Genma, Kishin, or Night.

General strategy:

• Transfer Tetra Break to your fastest unit, and have them cast it when the fight starts to remove the enemy's shield.
• After the shield is down, spam Phys attacks to hit the enemy's weaknesses. Try to ensure Tsukuyomi dies quickly, so he can't re-cast the shield.

Spike Hell Area (weak to Fire)

Overview

Mandrake	Heimdall	King Frost	Mandrake

Resistances
Mandrake	-	Wk	Wk	-	-	-	Nu
Heimdall	-	Wk	Nu	-	Dr	Nu	Rs
King Frost	-	Wk	Nu	-	-	Rs	-
Mandrake	-	Wk	Wk	-	-	-	Nu
Battle Speed			10,000

Skills on multiple demons:

Skills on Mandrakes only:

Skills on Heimdall only:

Skills on King Frost only:

Explanation

• Hellbound: Phys will apply 5 stacks of Spirit Chains of Suppression to you.
• Hell Eater drains your MP whenever your turn starts, and King Frost will drain your MP with Cold World Underside when he attacks (as well as applying ). When Heimdall falls below 50% HP, his Stout Horn Underside will also start draining your MP.
• If you fail to kill the adds by the start of their second turn, they will hit you with a bulwark-piercing, 100%-crit enrage AoE. Heimdall will do one too, if he isn't dead by his third turn - however his lacks phys pierce, so it can be reflected back at him with Repel Physical.

Fusibles challenge

Team restrictions:

Difficulty	Restriction
Lv 3-5	3 or more demons must be fusible*.
Lv 6-8	4 or more demons must be fusible.
Lv 9+	All 5 demons must be fusible.
Lv 6+	1 or more demons must be grade 79 (4★ base) or lower.
Lv 9+	1 or more demons must be Clear.

Notes regarding fusibles:

• Multi-fusions count.
  • Beelzebub☆ counts, despite needing a gacha-exclusive material to make him.
  • The following limited-time multi-fusions count: Masakado A, Alice A, Asura. All other limited-time multi-fusions do not count.
• Pixie and Slime count, even though you cannot fuse them.

General strategy:

• For level 9+, you need to run a team of all fusibles, with a focus on Fire damage. One of your demons must also be Clear, and one must be grade 79 or lower (meaning 4★ or lower base rarity).
• Your primary objective is to kill King Frost with Fire attacks on the first turn. If you don't, then he will hit into your weaknesses (most fusible Fire attackers are weak to Ice), debuff your defense, and steal all your MP. The Mandrakes should go down easily afterwards, allowing you to isolate Heimdall.
  • Any team slots that aren't providing utility should deal Fire damage or boost it.
  • Cybele does good damage and has a fire damage aura for the team (+10% damage at base, upgraded to +20% at panel 3). She is also Clear, fulfilling that team requirement.
  • Panel 3 Metatron gives a +20% magic damage aura to the team. Transfer a Fire spell so he can contribute his own damage, as well.
• MP management is very tight in this fight, consider running Divine brands on as many demons as possible.
• Have Huang Long use Five Elements ( Repel Almighty Magic), which will stop Heimdall from using his unique Almighty attack. Now, Heimdall will resort to standard attacks.
  • If possible, have Huang Long at panel 4 for his magic damage aura (+20% magic dealt and -20% magic received for the party while under Repel Magic). In this case, cast Five Elements ASAP to help push damage against King Frost.
• Bring demons with innate Null/Repel/Drain Phys, or a Null Phys genome transferred. Heimdall doesn't have Phys Pierce, so as long as Repel Almighty Magic is active, he will be unable to attack anyone that blocks Phys. This applies to both his standard attacks and his enrage AoE, which are both Phys.
  • Example 5★ demons with innate NDR Phys: Teal Quetzalcoatl, Teal Gogmagog, Zaou-Gongen, Erlkonig, Fafnir, Masakado A, Beelzebub☆
  • If you cast Tetrakarn or use a Phys Reflector (for Repel Physical) just before Heimdall's enrage, then you can reflect it back at him, potentially dealing a lot of damage to finish him off. However, you cannot have both Repel Physical and Repel Magic active at the same time, so only take this chance if you are sure the reflect will kill Heimdall. If Heimdall survives, then he will be free to use his Almighty attack, and might kill you.
• For the 4★ slot:
  • Prometheus offers good fire damage. Red gets a cheap Maragidyne, while Purple gets Infinite Chakra for more MP recovery.
  • Girimekhala, Rangda, Hecatoncheires, Teal Wu Kong have innate NDR Phys.

Sample party

Huang Long Skills Speedster Tetrakarn Brands Divine Requirements Panel 4

Cybele Skills Fire Boost Back Attack Brands Divine Requirements Panel 3

Metatron Skills Butcher Maragidyne Brands Divine Requirements Panel 3

Prometheus Skills Merciless Blow Serial Killer Brands Divine Requirements Panel 3

Surt Skills Fire Boost Fire Amp Brands Divine Requirements Panel 3

Team notes:

• Everyone should have Divine brands, due to the tightness of MP in this fight.
• Huang Long for Repel Almighty Magic and his panel 4 magic damage aura. Yellow can also buff with Luster Candy to push more damage. He should go first in the party, so he can activate his magic damage aura ASAP.
• Cybele satisfies the Clear requirement, offers a team Fire damage aura (ideally the upgraded version at panel 3), and has good innate Fire skills.
• Metatron for his panel 3 magic damage aura. He also has Maragidyne so he can contribute his own damage.
• Prometheus satisfies the 4★ requirement, and does good Fire damage. Red gets a cheap Maragidyne.
• Surt pushes damage against King Frost.
• Remember to use Tetrakarn or use a Phys Reflector just before Heimdall does his Phys enrage!

Race challenge

Team restrictions:

Difficulty	Restriction
Lv 3-5	All 5 demons must be of the races Beast, Vile, Femme, Tyrant, or Godly.
Lv 6-8	All 5 demons must be of the races Beast, Vile, Femme, or Godly.
Lv 9+	All 5 demons must be of the races Beast, Vile, or Tyrant.

• Your primary objective is to kill King Frost with Fire attacks on the first turn. If you don't, then he will hit into your weaknesses, debuff your defense, and steal all your MP. The Mandrakes should go down easily afterwards, allowing you to isolate Heimdall.
  • Any team slots that aren't providing utility should deal Fire damage or boost it.
• MP management is very tight in this fight, consider running Divine brands on as many demons as possible.
• The featured races do not have access to Repel Almighty Magic, so you'll need to use a different method to survive Heimdall's Almighty attack spam. For example: Spirit Chains of Intimidation.
• If you cast Tetrakarn or use a Phys Reflector (for Repel Physical) just before Heimdall's Phys enrage, then you can reflect it back at him, potentially dealing a lot of damage to finish him off.

Sample party

Lost Name Skills Fire Boost Assassin Brands HP% Life or Divine Requirements -

Moloch Skills Fire Survivor Fire Boost Brands HP% Life or Divine Requirements -

Belial Skills Serial Killer Fire Boost Brands PATK% Divine Requirements -

Mada Skills Fire Slowda Fire Boost Brands MATK% Divine Requirements -

Surt A Skills Butcher Fire Boost Brands MATK% Divine Requirements -

Team notes:

• Lost Name is easily accessible, does good damage, adds a Press Turn, and applies Spirit Chains of Intimidation to help the team survive.
• Moloch provides a team-wide Fire damage aura.
• The remaining members are just whatever Fire users are available.
• Remember to use Tetrakarn or use a Phys Reflector just before Heimdall does his Phys enrage!

Other options worth considering:

• Mithras offers 40% reverse damage reduction for Fire/Light.

Grave Area (weak to Ice)

Overview

Shiki-Ouji	Mithras	Cybele	Shiki-Ouji

Resistances
Shiki-Ouji	Nu	Wk	Wk	-	-	Rs	Rs
Mithras	-	Dr	Wk	-	-	Nu	-
Cybele	-	Dr	Wk	-	Rs	Nu	Rs
Shiki-Ouji	Nu	Wk	Wk	-	-	Rs	Rs
Battle Speed			10,000

Skills on multiple demons:

Skills on Shiki-Oujis only:

Skills on Mithras only:

Skills on Cybele only:

Explanation

• Hellbound: Fire will apply 5 stacks of Spirit Chains of Suppression to you.
• If you fail to kill the adds by the start of their second turn, they will hit you with a bulwark-piercing, 100%-crit enrage AoE. Mithras will do one too, if he isn't dead by his third turn.
• Mithras will follow up with Covenant Bless Underside whenever he, his allies, or you use a Fire/ Light attack. The hit doesnt hurt, but it does heal Mithras and his party, which can prolong the fight. Cybele and the Shiki-Ouji on the right also have healing spells.

Low-grade challenge

Team restrictions:

Difficulty	Restriction
Lv 3-5	3 or more demons must be grade 83 or lower.
Lv 6-8	4 or more demons must be grade 83 or lower.
Lv 9+	All 5 demons must be grade 83 or lower.
Lv 6-8	1 or more demons must be grade 79 (4★ base) or lower.
Lv 9+	2 or more demons must be grade 79 (4★ base) or lower.
Lv 9+	1 or more demons must be grade 59 (3★ base) or lower.

General strategy:

• Bring as many Ice attackers as possible, and kill the adds first so they can't heal Mithras.
• If you have an Illuyanka with the skill Illuyanka (Underside), bring that, as it trivializes this fight.

Sample party

Illuyanka Skills Illuyanka (Underside) Ice Boost Brands MATK% Spell Requirements -

King Frost Skills Back Attack Auto-Taruka Brands MATK% Divine or Spell Requirements -

Ym Skills Merciless Blow Serial Killer Brands MATK% Divine or Spell Requirements -

Frost Ace Skills Ice Amp Merciless Blow Brands MATK% Divine or Spell Requirements -

Black Rider Skills Mabufudyne Ice Boost Brands MATK% Divine or Spell Requirements -

Team notes:

• Illuyanka's contribution mainly comes from his 80% Ice damage aura and his Ice AoE chain. He doesn't really need MP either, so he should run Spell brands and a damage booster.
• King Frost provides DEF Debuff via his skill Cold World, to help push the damage. We also give him Auto-Taruka for ATK Buff, ensuring we have a full offensive buff swing.
• The rest of the team are just Ice attackers that don't have open weaknesses to Fire or Light, to ensure Mithras can't get extra turns off them. Resist Fire or Resist Light can be transferred to patch weaknesses, if needed.

Sanzu River Area (weak to Light)

Overview

Chatterskull	Ixtab	Nidhoggr	Chatterskull

Resistances
Chatterskull	-	Dr	Wk	-	-	Wk	Nu
Ixtab	-	-	-	-	-	Wk	Rp
Nidhoggr	Nu	-	Nu	Wk	-	Wk	-
Chatterskull	-	Dr	Wk	-	-	Wk	Nu
Battle Speed			10,000

Skills on multiple demons:

Skills on Chatterskulls only:

Skills on Ixtab only:

Skills on Nidhoggr only:

Explanation

• Hellbound: Dark will apply 5 stacks of Spirit Chains of Suppression to you.
• Vengeance Blow - When a Chatterskulls is killed, it will cast an Almighty hit with Mortal on their attacker.
• Nastrond Underside - When an enemy dies, Nidhoggr gets a 20% HP Bulwark and an 80% HP heal. When the enemy turn ends, a random enemy gets revived at 100% HP.
• Yache Underside - When Ixtab is killed, she will deal 40,000 fixed damage + Mortal + ignore endures. The gist is that she will wipe your party unless she dies last.
• If the adds are not dead at the start of their second turn, they will hit you with a bulwark-piercing, 100%-crit enrage AoE. Ixtab will do one too, if she isn't dead by his third turn.

Low-grade challenge

Team restrictions:

Difficulty	Restriction
Lv 3-5	3 or more demons must be grade 83 or lower.
Lv 6-8	4 or more demons must be grade 83 or lower.
Lv 9+	All 5 demons must be grade 83 or lower.
Lv 6-8	1 or more demons must be grade 79 (4★ base) or lower.
Lv 9+	2 or more demons must be grade 79 (4★ base) or lower.
Lv 9+	1 or more demons must be grade 59 (3★ base) or lower.

General strategy

• Set up Evade Mortal (with Tetraja, for example) as soon as possible, and refresh it when it runs out. Make sure it's active to shield the revenge Mortal hit whenever you kill something.
• Bring as many Light attackers as possible. Try to kill Nidhoggr first (so no revives can occur), then kill the Chatterskulls, and kill Ixtab last.

Sample party

Sukuna-Hikona Skills Tetraja Light Boost Brands MATK% Divine or Spell Requirements -

Mastema Skills Light Boost Serial Killer Brands MATK% Divine or Spell Requirements -

Lailah Skills Back Attack Serial Killer Brands MATK% Divine or Spell Requirements -

Baldur Skills Serial Killer Light Prana Brands MATK% Divine or Spell Requirements -

Ishtar Skills Light Boost Merciless Blow Brands MATK% Divine or Spell Requirements -

Team notes:

• Tetraja on the fastest unit, so we can cast it ASAP.
• Lailah does surprisingly good Light damage for a 3★. Red gives her Hamadyne as a single-target attack option.
• Baldur reduces the MP cost of the team's Light skills, and offers a small damage boost. Red gives him Mahamadyne as an AoE option. He's also a 4★, to help meet challenge requirements.
• Ishtar can set up buffs and debuffs, then switch to using Mahamaon afterwards.
• From there, just use whatever Light units are available, with whatever damage boosters you can.