Since: v0.16.0 — PR #20 — custom preset with raised y=32 floor v0.18.0 — PR #24 — 11-option Floor Y dropdown on the World tab (−64, −48, −32, −16, 0, 16, 32, 48, 64, 80, 96); y=32 remains the default v0.19.0 — PR #25 — preset is now default-selected when the Create World screen opens (via a client mixin into CreateWorldScreen.<init>) post-v0.74.0 — PR #105 — adds Dungeon Train (Nether) and Dungeon Train (End) as two new entries in the World Type dropdown; the chosen preset determines which dimension the player and starter train spawn in on first login v0.389.0 — PR #639 — removes Dungeon Train (Nether) and Dungeon Train (End) from the #minecraft:normal world-preset tag; new worlds can now only be created with an Overworld start. Existing Nether/End-start saves are unaffected — see Starting in the Nether or End below

Adds a custom world preset, Dungeon Train, selectable from the Create New World → More → World Type dropdown. It maps the overworld to a custom dimension whose floor sits at y=32 instead of vanilla's y=-64. Build height stays at y=320, so only the unused basement is removed — about 6 of 24 sub-chunk sections per chunk are eliminated.

For a train-on-rails game where players spend their time on the surface or aboard a moving Valkyrien Skies ship, the deep underground is wasted simulation. Removing it gives:

• CPU: ~24% fewer noise samples per chunk-gen — the preset ships its own noise_settings with noise.min_y=32, so the noise pipeline stops sampling discarded layers (not just the chunk dropping empty sections after the fact).
• Disk + RAM: ~15-20% smaller region files; fewer non-empty sections in memory.

1. Singleplayer → Create New World → More tab → World Type dropdown
2. Cycle through to Dungeon Train and create the world
3. Bedrock floor sits at y=32; everything above behaves like a vanilla overworld

For dedicated servers, set level-type=dungeontrain:dungeon_train in server.properties before first launch.

Kept	Lost
Surface terrain (mountains, rivers, oceans)	Deepslate ore zone (y=-64..0) — including diamonds and ancient-debris-equivalent ores
Iron, coal, copper, redstone (surface ore zones)	Lush + dripstone caves below y=32
All vanilla biomes (multi_noise)	Strongholds and mineshafts anchored below y=32
Vanilla nether and end (unchanged)	A small amount of cave detail near the new floor — hidden by the bedrock layer

PR #24 adds an 11-option Floor Y picker to the Create New World → World tab, visible only when the Dungeon Train preset is selected. The selection maps the world to one of eleven internal Y-variants at the moment the user clicks Create New World; the committed save then lives at the chosen floor height for its lifetime.

Dropdown options (multiples of 16):

Y	World range	Use case
−64	y=−64..320	Vanilla height — keeps all deepslate/diamond, no perf gain
−48	y=−48..320	Clip the bottom 16 blocks of the deepslate zone
−32	y=−32..320	Keep most deepslate ores, mild perf gain
−16	y=−16..320	Keep top half of deepslate
0	y=0..320	Keep surface ores only; sea-level floor
16	y=16..320	Slightly above sea level
32 (default)	y=32..320	Shipped v0.16.0 default — ~24% chunk-gen savings
48	y=48..320	Raised floor, preserves surface biome detail
64	y=64..320	Sea-level-equivalent floor
80	y=80..320	High floor, best perf
96	y=96..320	Extreme — most aggressive perf gain, smallest world

World top stays at y=320 for every option. Lower Y preserves more of the vanilla deepslate/diamond zone at the cost of chunk-gen savings; higher Y is cheaper but sacrifices ore layers.

Usage:

1. Singleplayer → Create New World → World tab
2. With World Type: Dungeon Train selected, the Floor Y row appears as a centered 150×20 CycleButton below Bonus Chest
3. Click through to the desired Y
4. Click Create New World

Dedicated servers: set level-type=dungeontrain:dungeon_train_y{N} (e.g. dungeontrain:dungeon_train_y0, dungeontrain:dungeon_train_y96) in server.properties before first launch. For the default y=32 use dungeontrain:dungeon_train (unchanged from v0.16.0).

The dropdown selection persists across Create-World screen entries within a single game launch, so re-opening the screen after a preset cycle restores the last chosen Y.

⚠️ Removed from new-world creation in PR #639 (v0.389.0). The Dungeon Train (Nether) and Dungeon Train (End) entries no longer appear in the Create World screen's World Type cycle — new worlds can only be created with an Overworld start. This section is kept for reference and for anyone maintaining a world that already started in the Nether/End; the underlying mechanism below is otherwise unchanged and those saves keep working exactly as before.

Two additional World Type entries — Dungeon Train (Nether) and Dungeon Train (End) — started the player and the auto-spawned train in minecraft:the_nether or minecraft:the_end instead of the overworld. Worldgen for those dimensions is vanilla — only the starting dimension changes; the overworld is still configured exactly like the plain Dungeon Train preset (raised y=32 floor) and remains accessible via portals.

Usage (legacy — no longer reachable from the Create World UI):

1. Singleplayer → Create New World → World tab
2. Cycle the World Type button to one of:
   • Dungeon Train — start in overworld (default, and now the only UI-selectable option)
   • Dungeon Train (Nether) — start in the Nether
   • Dungeon Train (End) — start in the End
3. Click Create New World — on first login the player is teleported to a random ground position alongside the train in the chosen dimension.

The Floor Y dropdown is hidden for the Nether/End presets (it only affects the overworld bedrock floor). The Dungeon Train Options… sub-screen still applies — Train Y, carriage dimensions, generation mode, and group size all work the same in any starting dimension.

Persistence: the chosen dimension is committed to dungeontrain_world.dat (the existing per-world SavedData) as a startingDimension NBT tag, defaulting to overworld for legacy worlds. This is why existing Nether/End-start saves are unaffected by the removal above — the preset files and the StartingDimension enum are all still in place; only the tag entry that made them reachable from a new Create World screen was removed.

Known limitations:

• Death/respawn is a separate mechanism, partially restricted since. StartingDimension.rollRespawnDimension independently rolled a fresh 94% Overworld / 5% Nether / 1% End dimension on every death. As of PR #643 (v0.390.0), the death screen's "New World"/"Same World" buttons (DeathScreenLayoutHandler, plus the dev-only /new-world command which shares the same code path) always start the fresh save in the Overworld — they create a new world, so the same "Overworld by default" intent as this page applies. The vanilla in-place "Respawn" button (RespawnDimensionEvents) is intentionally unchanged and still rolls the 94/5/1 split, since it's a deliberate run-variance mechanic that doesn't create a new world. See Feature-Death-Screen-Buttons for the full mechanism.
• Default Train Y (78) in the End places the train above the central island; in the Nether it sits well above the lava ocean and below the ceiling. Both can be overridden via the Dungeon Train Options sub-screen if the user wants a different elevation for that biome.

Dedicated servers: level-type=dungeontrain:dungeon_train_nether or dungeontrain:dungeon_train_end in server.properties still works for anyone who sets it explicitly (the preset registry entry still exists) — only the graphical World Type cycle button no longer surfaces these two options.

File	Purpose
data/dungeontrain/dimension_type/overworld.json	Default DimensionType with min_y=32, height=288 (y=32 preset)
data/dungeontrain/dimension_type/overworld_y{N}.json (10 files)	Y-variant DimensionTypes; min_y=N, height=320-N
data/dungeontrain/worldgen/noise_settings/overworld.json	Vanilla overworld noise_settings with noise.min_y=32, noise.height=288
data/dungeontrain/worldgen/noise_settings/overworld_y{N}.json (10 files)	Y-variant noise_settings (only noise.min_y + noise.height differ)
data/dungeontrain/worldgen/world_preset/dungeon_train.json	Default preset (y=32); nether/end reference vanilla
data/dungeontrain/worldgen/world_preset/dungeon_train_y{N}.json (10 files)	Y-variant presets referencing the matching DimensionType + noise
data/dungeontrain/worldgen/world_preset/dungeon_train_nether.json	Same dimension config as dungeon_train.json; the preset ID is the marker that signals "start the player in the Nether" (PR #105)
data/dungeontrain/worldgen/world_preset/dungeon_train_end.json	Same shape as the Nether variant; signals "start in the End" (PR #105)
data/minecraft/tags/worldgen/world_preset/normal.json	Lists only dungeon_train as of v0.389.0 (PR #639) — dungeon_train_nether/dungeon_train_end were removed so the UI selector shows one entry; both preset files still exist and resolve by key for legacy saves + the death-screen carry-forward flow. Y-variants remain intentionally out of the tag (the registry resolves them by key instead)
src/.../world/StartingDimension.java	Enum mapping preset path → dimension ResourceKey<Level> and NBT id (PR #105)
src/.../client/worldgen/PendingStartingDimension.java	Client-side static holder (mirrors FloorYState); updated each tick from the current preset path; consumed once on integrated-server start (PR #105)
assets/dungeontrain/lang/en_us.json	generator.dungeontrain.dungeon_train* keys all resolve to "Dungeon Train" so the preset button label stays consistent; dungeontrain.floor_y.* keys for the widget label/value/tooltip
src/.../mixin/CreateWorldScreenWorldTabMixin.java	@Inject at <init> TAIL of CreateWorldScreen$WorldTab; appends the Floor-Y row at hardcoded row index 5
src/.../mixin/CreateWorldScreenMixin.java	init TAIL resolves the 11 preset holders into FloorYState; tick HEAD toggles widget visibility + re-applies the chosen Y on transitions back onto the plain DT preset
src/.../mixin/CreateWorldScreenAccessor.java	@Accessor exposing the package-private uiState field
src/.../client/worldgen/FloorYState.java	Client-side static holder for selected Y + per-screen widget + preset-holder map

• Disk footprint: ships 10 near-identical copies of the 2,541-line noise_settings/overworld.json (one per non-default Y), ~900 KB uncompressed. A refactor to dynamic runtime registration (approach b from the Gate 1 plan) is tracked as a follow-up if size becomes an issue.
• Preset cycling quirk: cycling the World Type button forward while a Y-variant is active falls back to the plain dungeon_train preset (vanilla's values.indexOf(current) returns −1 when the Y-variant isn't in the selector list, so it resets to index 0). From there, one more forward-cycle reaches Default. The tick handler explicitly does not re-apply Y when the user has just cycled from one DT variant to another — only on transitions from a non-DT preset back onto DT.
• Vanilla density functions still reference absolute Y, so the new floor may produce small swiss-cheese caves just above bedrock — visually hidden, no gameplay impact.
• Existing worlds are unaffected. Only new worlds created with the Dungeon Train preset get the raised floor. Vanilla saves continue to work normally. Worlds created with a non-default Y on v0.18.0+ require the mod at v0.18.0 or later to continue loading (normal mod-version behavior; no migration).