The Undertale 10th Anniversary Website: 5 Biggest Surprises & New Sans Fight Details

The 10th Anniversary of *Undertale* is a monumental occasion for indie gaming, and creator Toby Fox has not disappointed with a massive slate of announcements, including a dedicated anniversary website that serves as a hub for the celebration. As of December 16, 2025, the official *Undertale* 10th Anniversary website is live, detailing a year-long event that goes far beyond simple merchandise. This in-depth look explores the biggest revelations, from a brand-new in-game challenge to a collaboration with a legendary gaming studio. The celebration centers around the official website, which is the key to unlocking all the new content and events. The site, alongside the latest *UNDERTALE*/ *DELTARUNE* newsletter, has confirmed a two-day live stream, a major orchestral concert, and a unique way for the community to share their deepest memories of the groundbreaking RPG. If you thought the game's ninth anniversary was big, the tenth is truly a game-changer.

The Ultimate Guide to Undertale's 10th Anniversary Celebration (2025)

*Undertale* was first released on September 15, 2015, making 2025 its official tenth anniversary. The celebration is not just a single-day event but a multi-faceted tribute to one of the most influential indie games of all time. The core of the celebration is the official Undertale 10th Anniversary Website, which directs fans to various parts of the event.

1. The New Sans Fight and Challenging New Foes

The most exciting revelation for veteran players is the confirmed addition of new in-game content accessible via the anniversary website. Reports indicate that the celebration includes a dedicated feature on the site that allows players to face Sans, along with some brand-new foes. This is a massive development, as the original Sans fight is legendary in the gaming community for its difficulty and emotional weight. A new fight or a remixed version suggests a fresh challenge for those who have mastered the Genocide Route. The inclusion of "new foes" also hints at a small, self-contained experience that expands the *Undertale* universe in a surprising way, directly from the creator, Toby Fox. * The Challenge: A new, presumably non-canon, battle with Sans. * New Entities: The introduction of unspecified new enemies. * Accessibility: The content is linked directly to the anniversary website.

2. The Memories Hub: memories.undertale.com

Toby Fox launched a specific subdomain, memories.undertale.com, as a digital scrapbook for the community. This interactive website asks a simple yet profound question: "What does *Undertale* mean to you?" This initiative is a beautiful nod to the game's focus on player choice and emotional resonance. Fans are encouraged to submit their favorite memories, emotional connections, or artistic creations inspired by the game. The goal is to collect and showcase these stories, creating a collective, living tribute to the game's impact over the last decade. This focus on player memories highlights the game's legacy as a cultural phenomenon, not just a game.

3. Two-Day Official Live Stream Event

To mark the actual anniversary date, a major two-day live stream event has been scheduled for the 20th and 21st (likely September 2025). The stream will be watchable on the official site, Undertale.com/10/, and via the Fangamer Twitch account. The main feature of this stream is a full playthrough of *Undertale*, mirroring a previous stream where the team played through *DELTARUNE* Chapter 1. This event offers a chance for the community to re-experience the game together, likely featuring commentary, behind-the-scenes stories, and possible new announcements from Toby Fox himself. Expect appearances from key members of the development and music team, including the original musician, to discuss the game's creation and impact.

4. Major Orchestral Concerts: The Determination Symphony

The music of *Undertale* is just as iconic as its characters, and the 10th anniversary is being celebrated with multiple high-profile musical events. * The Determination Symphony: A one-night-only live orchestral concert is scheduled, with tickets for this major event going on sale in March 2025. This concert will bring the beloved soundtrack, featuring tracks like "Megalovania," "Hopes and Dreams," and "Spear of Justice," to life with a full symphony orchestra. * Official 10th Anniversary Concert: A separate, official *UNDERTALE 10th Anniversary Concert* has also been announced, complete with its own dedicated website. This suggests a global or multi-city concert series, catering to the massive international fanbase. These events are a powerful testament to the timeless quality of the game's score.

5. Square Enix Music & Merchandising Collaboration

In a surprising and high-profile move, *Undertale* is collaborating with Square Enix Music & Merchandising to celebrate the anniversary. Square Enix is a titan of the RPG genre, known for franchises like *Final Fantasy* and *Dragon Quest*. This collaboration promises new music releases, unique apparel, and potentially "things a little strange," as described in the official announcement. The partnership with a major Japanese publisher like Square Enix underscores *Undertale's* massive influence in the JRPG-loving community and promises high-quality, collectible merchandise that fans will undoubtedly clamor for. This move solidifies *Undertale's* place among the pantheon of great RPGs.

The Future: Deltarune and the Toby Fox Newsletter

While the focus is on *Undertale*, the anniversary celebration naturally ties into the future of the franchise, specifically *DELTARUNE*. Toby Fox used the anniversary to release a brand new *UNDERTALE*/ *DELTARUNE* newsletter. The newsletter, a traditional method for Fox to communicate with his fans, provides updates on the development of *DELTARUNE* Chapter 3 and beyond. This is crucial for fans eagerly awaiting the next installment of the parallel story. The anniversary serves as a perfect platform to generate buzz for the next chapter, ensuring that the celebration of the past also fuels excitement for the future. The massive scale of the 10th-anniversary events—from the new Sans fight to the Square Enix partnership—demonstrates that *Undertale*'s legacy is stronger than ever. Fans are encouraged to check the official Undertale 10th Anniversary Website frequently for ticket sales, stream schedules, and the latest news from Toby Fox.