The experience grew by Underground regions. Dates below are the days footage showed a region as playable, or the day a code and later discussion used the name. They are not developer patch timestamps.
Order players actually entered
- Ruins was the opening region in August 2024. Early units named with it include Froggit, Migosp, and Loox. Gauntlet mode was already a separate repeatable fight, and an August 10, 2024 tour farmed it for soul fragments, trait rerolls, and perfect souls.
- Snowdin was shown as the live update in footage published August 9, 2024. The summon banner in that tour listed Ice Cap and Doggo as commons, Dogamy, Dogaressa, and Snowdrake as rares, Greater Dog and Lesser Dog as super rares, and Papyrus as the ultra rare. Chill Glasses from Snowdin drops were the item used to evolve Snowdrake into Chill Drake. Grillby was shown as a money-unit drop, not as part of that summon list.
- Waterfall was shown as live in footage published September 21, 2024. That tour added a Waterfall summon, the Underpass track, and a ninth-anniversary raid of 25 waves that paid candles used to open gift skins. Act 6 Neutral footage from September 25, 2024 shows flying enemies at the start and longer waves than earlier acts.
- Hotland is named by the expired code HOTLANDS2025 and by 2025 player questions about kill grinds. A June 11, 2025 unofficial changelog listed a Hotlands banner with Vulkin, Tsunderplane, Heats Flamesman, Pyrope, Royal Guard 01, Royal Guard 02, Alphys, Mettaton, and Muffet. That roster was not checked against the October 2026 build. Muffet and the Mettaton forms are still in October 2026 role tables.
- Core is the later area players named next to Hotland when asking where to grind kills. An August 2024 tour also walked through the Core to reach the MTT Hotel and the AFK Chamber. No October 2026 act list was published.
Other modes that were shown
- Gauntlet is an endless-style repeat fight used for shop currency in August 2024. Bosses could spawn during it.
- Infinite mode is the endless score run from the September 24, 2024 beginner guide. The current listing does not mention it.
- Anniversary raid is the 25-wave candle event inside the September 21, 2024 Waterfall footage. Skins from those gifts included party colors for Loox, Greater Dog, Woshua, and the unit the caption called Dapper B.
- Christmas event appears in a January 2, 2026 upload with Easy and Hard modes, an event shop, summons, a pastry shop, and Prestige Sansta. The uploader said the video was late, so January 2 is not the event start. The October 2026 listing title is the Release version, not the older Christmas title.
- TS!Underswap was a limited boss event in footage from November 29, 2024, with TS!Sans, TS!Papyrus, and a ketchup blaster item. Perseverance's buff to +20% range and +20% damage was stated in that same video.
How to pick an act
An August 3, 2024 prep video said every act at that time paid the same XP and Souls, so Act 1 Neutral was the fast XP clear, while a later Genocide act was the drop farm. Snowdin's own notes said trait materials became harder after that update and stopped dropping from ordinary stage clears. Do not use the "all acts pay the same" line for Waterfall or later. The September 25, 2024 Act 6 footage already describes longer waves.
Region pages are under Worlds. Historical equipment from the Snowdin drops is under Equipment.