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Underpass

Underpass

Wave-XP reward track still named by the Supporter pass.

Underpass in [🎉RELEASE🎉] Undertale Adventures X

Underpass: Wave-XP reward track still named by the Supporter pass. Get it by Play stages and clear waves. Supporter adds 15% Underpass XP if you own that pass. Use it to Level the track by clearing waves if the lobby still shows it. Do not buy Supporter for a Neo reward that was only shown in 2024 footage.

By [🎉RELEASE🎉] Undertale Adventures X WikiLast updated:

What is Underpass?

The Underpass is a long reward track shown in Waterfall update footage published September 21, 2024. XP came from waves cleared, and higher tiers opened rewards. That footage called a premium side Underpass Neo and treated Chara as a unit from the premium track. The October 2026 Supporter pass still grants 15% more Underpass XP, plus a 10% summon discount, a title, and a chat tag. It does not restate the Neo reward list.

Published facts

FactValue
How it advancesXP from waves cleared

How do you get Underpass?

Play stages and clear waves. Supporter adds 15% Underpass XP if you own that pass.

How do you use Underpass?

Level the track by clearing waves if the lobby still shows it. Do not buy Supporter for a Neo reward that was only shown in 2024 footage.

FAQ

Underpass questions

What is Undertale Adventures X?

It is a free Roblox tower defense experience by Side Productions. You defend a base with Undertale-inspired units, level those units, and strengthen them with traits. The experience was created on July 16, 2024, and the public record was updated on October 12, 2026.

Is Undertale Adventures X free?

The Roblox listing has no paid entry price. Optional Robux gamepasses exist. Known names include VIP, SHINY Hunter!, Supporter, +50% Tokens, and 2x XP. Current Robux prices were not on the public listing text used here.

Who makes the game?

Side Productions, the verified Roblox community that owns the experience. The community page is linked from the game listing.

How do codes work?

Open the Codes button on the right side of the screen, enter the full string, and press Enter or Redeem. Only 2KCCU! and FREESTUFF! were still reported working in October 2026, and both rewards were described only as freebies.

Do trait rates still match the old table?

Trait rerolls assign one of 12 listed traits. The rate table matches an August 2024 odds screen for Royal Guard Soul at 15%, and a November 29, 2024 video described the Perseverance buff the table now shows. Read the percent in your own Traits menu before you spend a large stack of rerolls.

Related
GuideClear your first defenseHow a first defense works: what the October 2026 Roblox listing confirms, and which placement, money, and difficulty rules come from 2024 footage.Read guideGuideTraits, rerolls, and stat lettersAll 12 listed trait rates and effects, which early souls are worth keeping, and how that table relates to the August 2024 odds screen.Read guideGuideRaids, tokens, AFK, and passesRaids tokens, the Underpass track, the AFK Chamber, and the five named gamepasses, with 2024 shop prices kept separate from 2026 perk text.Read guideCategoryAll UnderpassRead guideCodes[🎉RELEASE🎉] Undertale Adventures X CodesActive, redeem, and expired lists.Read guideVideos[🎉RELEASE🎉] Undertale Adventures X Video TutorialsWatch practical walkthroughs and progression tips.Read guideCodesHow to redeem [🎉RELEASE🎉] Undertale Adventures X codesWhere a redeem box would appear after a patch.Read guideCodesExpired [🎉RELEASE🎉] Undertale Adventures X codesRetired strings and why fake lists stay empty.Read guideTools[🎉RELEASE🎉] Undertale Adventures X toolsEditorial pickers and calculators.Read guideTools[🎉RELEASE🎉] Undertale Adventures X class pickerPublished roster topics for reference.Read guide
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See also

Same topic[🎉RELEASE🎉] Undertale Adventures X databasereferenceRead guideSame topic[🎉RELEASE🎉] Undertale Adventures X UnitsreferenceRead guideSame topic[🎉RELEASE🎉] Undertale Adventures X TraitsreferenceRead guideSame topic[🎉RELEASE🎉] Undertale Adventures X WorldsreferenceRead guideSame topic[🎉RELEASE🎉] Undertale Adventures X EquipmentreferenceRead guideSame topic[🎉RELEASE🎉] Undertale Adventures X TokensreferenceRead guide