Hell's Park Underside

Hell's Park Underside is a mode where you fight bosses that have customizable difficulty levels. It is unlocked after clearing all 100 "surface" stages of Hell's Park.

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.

Each area is weak to a specific element, and has 3 possible rulesets for which kinds of demons you can bring in. 3 areas are available each month, and the available ruleset for each area also changes each month.

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.

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.
• Press Turn Generation and Press Turn Removal do not work.
• Press Turn Retention (such as Chief God's Rage or Tag) do not work.
• Remnants and Critical Hits will not use half a Press Turn, unless they also hit a weakness.
• 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.

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 rewards stop being given from level 501 onwards.

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.

• Levels 501 onwards do not give any rewards.

Level	Silver per level
11-20	300
21-100	50
101-500	10

Score and ranking

When you clear a battle in Hell's Park Underside, you'll earn a score based on your performance. Score is awarded based on several factors:

• The level of the battle cleared (the higher, the better).
• Clearing the battle in a small amount of turns.
• Having unused Press Turns remaining.
• Dealing a lot of total damage.

Your score will be assigned a letter rank, based on how high it is:

Rank	score
SSS	1,200,000+
SS	600,000-1,199,999
S	300,000-599,999
A	125,000-299,999
B	68,500-124,999
C	38,500-68,499
D	26,500-38,499
E	17,500-26,499
F	11,500-17,499
G	0-11,499

Ranking rewards

silver badges will be rewarded each month, based on how your score ranks against other players.

Per-area score ranking rewards

Rank	Reward
1-10	silver badge x1,000
11-100	silver badge x500
101-1,000	silver badge x400
1,001-10,000	silver badge x300
10,001-30,000	silver badge x200
30,001-9,999,999	silver badge x100

Total score ranking rewards

Rank	Reward
1	silver badge x3,000, "Underside MVP" title
2	silver badge x3,000, "Proven Strength" title
3	silver badge x3,000, "A True Secret Trick" title
4-10	silver badge x3,000, "Famous Behind the Scenes" title
11-100	silver badge x1,500
101-9,999,999	silver badge x1,000

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	Baphomet (Underside)	Spike Hell Area only	Baphomet	Available through silver badges in Apr 2025.
Passive	Arianrhod (Underside)	Sanzu River Area only	Arianrhod	Available through silver badges in May 2025.
Passive	Dominion (Underside)	Blood Pond Area only	Dominion	Available through silver badges in Jun 2025.
Passive	Jack Frost (Underside)	-	Jack Frost	Available through silver badges (Jun 2025 onwards)
Passive	Scathach (Underside)	Hell Cafe Area only	Scathach	Available through silver badges in Jul 2025.
Passive	Shiki-Ouji (Underside)	Sanzu River Area only	Shiki-Ouji	Available through silver badges in Aug 2025.
Passive	Mermaid (Underside)	Spike Hell Area only	Mermaid	Available through silver badges in Sep 2025.
Passive	Baihu (Underside)	Burning Area only	Baihu	Available through silver badges in Oct 2025.
Passive	Kaiwan (Underside)	Blood Pond Area only	Kaiwan	Available through silver badges in Nov 2025.
Passive	Efreet (Underside)	Hell Cafe Area only	Efreet	Available through silver badges in Dec 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)
Elec	Thunder Reign (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Elec	Thunder Slash (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Force	Killing Wind (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Force	Wind 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)
Dark	Hell Gaze (Underside)	-	-	Rare drop from Hell Genome Cube (costs silver badges)
Dark	Black 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 690 per month (230 per area) if 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 (rotating)
Illuyanka (Underside) Genome	3,000	1 (rotating)
Koumokuten (Underside) Genome	3,000	1 (rotating)
Baphomet (Underside) Genome	3,000	1 (rotating)
Arianrhod (Underside) Genome	3,000	1 (rotating)
Dominion (Underside) Genome	3,000	1 (rotating)
Jack Frost (Underside) Genome	3,000	1
Scathach (Underside) Genome	3,000	1 (rotating)
Shiki-Ouji (Underside) Genome	3,000	1 (rotating)
Mermaid (Underside) Genome	3,000	1 (rotating)
Baihu (Underside) Genome	3,000	1 (rotating)
Kaiwan (Underside) Genome	3,000	1 (rotating)
Efreet (Underside) Genome	3,000	1 (rotating)
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

• Silver badge income is 7,200 per month (2,400 per area) if you clear level 10 of each area.
  • If you clear level 20 of each area, add 9,000 (3,000 per area) to that.
  • Each set of 10 levels from level 21-100 gives 1,500 (500 per area).
  • Each set of 10 levels from level 101+ gives 300 (100 per area).
  • Assuming you are in the lowest ranking tier, you can expect another 1,300 per month (1,000 for total score, plus 100 per area).

Hell Genome Cube

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
Thunder Reign (Underside)	Rare, exclusive
Thunder Slash (Underside)	Rare, exclusive
Killing Wind (Underside)	Rare, exclusive
Wind Slash (Underside)	Rare, exclusive
Thunderclap (Underside)	Rare, exclusive
White Slash (Underside)	Rare, exclusive
Hell Gaze (Underside)	Rare, exclusive
Black 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 (Fire)	Kawara (Phys) (Kishin, Genma, Night)	Grave (Ice)	Pixie (Underside)
Feb 2025	Spike Hell (Fire)	Kawara (Phys) (Kishin, Genma, Night)	Grave (Ice)	Illuyanka (Underside)
Mar 2025	Kawara (Phys)	Spike Hell (Fire) (Beast, Vile, Tyrant)	Sanzu River (Light)	Koumokuten (Underside)
Apr 2025	Blood Pond (Elec)	Sanzu River (Light) (Holy, Megami, Deity)	Spike Hell (Fire)	Baphomet (Underside)
May 2025	Sanzu River (Light)	Hell Cafe (Force) (Lady, Genma, Avian)	Blood Pond (Elec)	Arianrhod (Underside)
Jun 2025	Hell Cafe (Force)	Blood Pond (Elec) (Megami, Night, Divine)	Kawara (Phys)	Dominion (Underside)
Jul 2025	Grave (Ice)	Kawara (Phys) (Kishin, Fairy, Fiend)	Hell Cafe (Force)	Scathach (Underside)
Aug 2025	Kawara (Phys)	Sanzu River (Dark) (Tyrant, Vile, Brute)	Grave (Ice)	Shiki-Ouji (Underside)
Sep 2025	Sanzu River (Dark)	Grave (Ice) (Dragon, Femme, Megami)	Spike Hell (Force)	Mermaid (Underside)
Oct 2025	Burning (Elec)	Spike Hell (Force) (Megami, Genma, Avian)	Sanzu River (Dark)	Baihu (Underside)
Nov 2025	Spike Hell (Force)	Blood Pond (Dark) (Vile, Fallen, Night)	Burning (Elec)	Kaiwan (Underside)
Dec 2025	Blood Pond (Dark)	Burning (Elec) (Holy, Deity, Kishin)	Hell Cafe (Fire)	Efreet (Underside)

Guide pages

Hell's Park Underside
Area	Phys	Fire	Ice	Elec	Force	Light	Dark
Spike Hell	-	Spike Hell (Fire)	-	-	Spike Hell (Force)	-
Kawara	Kawara (Phys)	-	-	-	-	-	-
Grave	-	-	Grave (Ice)	-	-	-	-
Sanzu River	-	-	-	-	-	Sanzu River (Light)	Sanzu River (Dark)
Blood Pond	-	-	-	Blood Pond (Elec)	-	-	Blood Pond (Dark)
Hell Cafe	-	Hell Cafe (Fire)	-	-	Hell Cafe (Force)	-	-
Burning	-	-	-	Burning (Elec)	-	-	-