Here is a concise summary of the provided text:
**Game Development & Basics**
* Undertale, a visually simplistic RPG, was developed independently by Toby Fox.
* Initially, a demo was released in 2013, followed by a Kickstarter campaign that exceeded its goal.
* The game was released on September 15, 2015, to critical acclaim.
**Gameplay Secrets & Easter Eggs**
* Various hidden elements, such as:
+ Audible voice clips for Flowey and Mettaton.
+ A hidden area with a quiche, referencing Homestuck.
+ An abandoned "flower bridge" area.
+ A long-necked Lesser Dog sculpture.
+ Sans selling Hot Dogs, with a stacking glitch.
+ Papyrus' kitchen interaction loop.
**Sans' Awareness & Theories**
* Sans seems aware of different timelines and the player's actions.
* Exhibits strange abilities, possibly teleportation or time manipulation.
* His dialogue suggests knowledge of the game's nature.
**W.D. Gaster Theories**
* A mysterious, mostly unseen character, accessible by editing game files.
* Possibly stands for "Wing Dings Gaster" due to hidden font clues.
* May be related to Papyrus and Sans, who are named after typefaces.
* Various indirect references throughout the game.
**Game Design & Cut Content**
* Speculation that Gaster's content was cut from the final game.
* Examples of hidden, unused game files and dialogue.
* Undertale's unique aspect: breaking the fourth wall, incorporating game mechanics into the storyline.
Here are the key facts extracted from the text, keeping them short and without opinions:
**Game Development & Release**
1. Undertale was developed independently by Toby Fox.
2. A demo was sent to Fangamer in May 2013, which received mostly positive reviews.
3. A Kickstarter campaign was launched in June 2013, exceeding the $5000 goal by over 10 times.
4. The game was initially expected to be around 2 hours long but ended up being over 3 times as long.
5. Undertale was released on September 15, 2015.
**Gameplay & Mechanics**
6. The game's story is told entirely through text, similar to classic RPGs.
7. Two characters, Flowey and Mettaton, have audible speech in specific instances.
8. A hidden area can be accessed in Waterfall by ignoring a puzzle and taking flowers to the bottom right of the screen.
9. Repeatedly walking in and out of the kitchen in Papyrus' and Sans' house triggers a unique interaction.
10. Playing the Pacifist Route and completing the end credits minigame unlocks the Mysterious Door in Snowdin Forest.
**Characters & Lore**
11. Sans is aware of the existence of different timelines and the player's actions.
12. Sans exhibits strange abilities, such as teleportation, in specific scenes.
13. W. D. Gaster is a mysterious character almost never seen nor mentioned in normal gameplay.
14. Gaster was the Royal Scientist before Alphys, created the CORE, and presumably disappeared into it.
15. The names Papyrus and Sans are derived from the typefaces Papyrus and Comic Sans, potentially indicating a relation.
**Easter Eggs & Hidden Content**
16. A hidden message can be found in the game's official website's HTML code.
17. Modifying game files reveals a hidden section in the True Lab with a message in Wingdings font.
18. Naming the character "GASTER" at the beginning causes the game to restart.
19. A hidden stage called Sound Test contains four unique loops, including "Gaster's Theme".
20. A blueprint in Sans' room features symbols that may relate to a machine, potentially written in Wingdings by Gaster.