ArcalithTale Master Post
ArcalithTale is a Undertale AU that in which monsters can condense their innate magic into crystalline forms known as Crysalith. These gems act as external magical conduits, stabilizers, and power focuses, tailored to each monster’s species and personal affinity.
In ArcalithTale, every monster receives their Crysalith at age ten. This crystallized magic is not their SOUL, but is magically bound to them.
In my case, this also added the fact that it's a crossover AU with Harry Potter. ArcalithTale start to diverges from the typical Undertale AU timeline just a few years after W. D. Gaster fell into the Core, when Sans take a stroll after having a burger at Grillby's, he found a tiny babybones who look no older that 5 years old (by monster standards) buried in snow near the forrest of Snowdin. He later found out that the babybones is a Shifter; a human Sage (nowdays called themselves Wizards & Witches) who died while their magic, in effort to save themself, shifted their very being into a Monster type that compatible with them. And that is how the Font brothers gain a new sibling.
My works of this AU in AO3, Wattpad, & Fanfiction.net. On that note, I'll update my work every week on Thursday on those platforms.
P.S. I'm sorry, but for a while there will be no fanart for this AU, I can't draw anything decent yet so please bear with me. Thanks!
All posts can be found under the #ArcalithTale AU tag.
P.S. starting 7 September 2025 I rename this AU from GemTale to ArcalithTale due to finding out that there is already an AU named GemTale before I made this AU.
Details below + Links:
Character Biodata & Short Background Story:
Sans
Papyrus
Avallon
Frisk
Chara
Asriel
Asgore
Toriel
Grillby
Mettaton
Muffet
Gaster
AU Lore(s):
Crysalith
Shifter
General Timeline
Work(s):
• Jaded Emerald:
Arc I: Prologue, AO3 [Prologue, Chapter 1, Chapter 2, Chapter 3, Chapter 4, Chapter 5, Chapter 6, Chapter 7, Chapter 8, Chapter 9, Chapter 10, Chapter 11, Chapter 12, Chapter 13, Chapter 14, Chapter 15, Chapter 16, Chapter 17, Chapter 18, Chapter 19, Chapter 20, Chapter 21, Chapter 22]
Arc II: AO3 [Prologue, Chapter 1, Chapter 2, Chapter 3, Chapter 4, TBC...]