Not much would make an Azkaban escape become second page news among the Wizards of the United Kingdom, but the freeing of the Monsters under Mount Ebott would do it. And thus Frisk becomes one of Hogwart's newest, first year, students...
Harry Potter and the Underground's Saviour is a crossover fanfiction between Harry Potter and Undertale by TheZorker. It starts with Frisk going to Hogwarts School of Wizardry after freeing the monsters before Harry's third year and things escalate from there.
The original fanfic is available here. (Complete)
The sequel, Harry Potter and Endless Possibilities, can be found here. (Complete)
The 3rd installment, Harry Potter and the Muggles Who Needed Magic can be found here.
In Harry Potter and the Underground's Saviour, Frisk attends Hogwarts with many iconic Harry Potter characters. Not getting over somethings that have happened in the Underground, mainly Asriel's death, Frisk tries her best to fit in with the other Hogwarts students, while learning of both the many problems the school has, and of something that just might save Asriel.
In Harry Potter and Endless Possibilities, Frisk attends another year at Hogwarts with a surprising twist of fate seeing as Asriel, now fully revived, is now attending the school, alongside fellow sibling Chara Dreemurr, also meant to be dead, whilst the Tri-Wizard Tournament goes on.
Provides Examples of:
- Abusive Parents: Chara's old parents (being Malfoys, as Chara is Draco's cousin) are. They intended Chara to die by sending her to Mt. Ebott.
- Academy of Adventure: Obviously, it's Hogwarts.
- Achey Scars: Frisk has quite the amount of leg fractures from her two long falls in the timeline she kept. All it takes is one kick with the intent to hurt to practically shatter Frisk's leg.
- Badass Family: The Dreemurrs.
- Barred from the Afterlife: Asriel, Chara, and W.D Gaster.
- Beyond the Impossible: As pointed out in chapter 24 of Underground's Saviour, bringing back a wizard from the dead is near impossible, even by wizard standards. We learn later that Chara was only able to come back because her soul had not moved on, having been tied to Frisk's
- Back from the Dead: Chara and Asriel by the end of Book one. Gaster from Book Two.
- Broad Strokes: Not much is known about Gaster, or Chara in game, and thus the author flies with the ideas that Gaster is Sans' and Papyrus' father, and that Chara is a Malfoy.
- Color-Coded for Your Convenience: As per usual in Undertale lore, the traits of multiple Human souls. Yellow for justice, Green for kindness, etc.
- Completely Off-Topic Report: Downplayed, but serious, Frisk takes exception to having to write about how to kill werewolves, and writes about their humanity instead. Snape is not pleased.
- Downer Ending: As of chapter six, Frisk believes the original game to have had this; possibly do to Boggart and Dementor influence.
- Empowered Badass Normal: Being a first year and all, Frisk is still a badass in their own rights.
- Evil Makes You Ugly: Implied with Monster Soul magic.
- Excuse Plot: Averted; Frisk, Chara, and Asriel are all placed in Gryffindor, but the author says in a couple of author's notes that he took their personalities into extreme consideration before placing them there in order to avoid invoking this trope.
- The Faceless: Dementors, as per usual in Harry Potter lore.
- Fate Worse than Death: Asriel's fate mimics the fate of someone subjected to the Dementor's kiss, as per usual in lore. Goes in depth in chapter 5.
- Gaster's being stuck in Limbo.
- Glowing Eyes of Doom: Inverted with Sans, like in the game. It's when his eyelights go out that you know he's serious.
- Handicapped Badass: Asriel in his own rights. While he is still getting used to walking after being a soulless flower, he's still able to convince Chara to come back.
- Jerkass: Cormac McLaggen, Draco Malfoy, and Snape all in their own rights, and as per usual in canon.
- Heart Broken Badass: Frisk is especially this before Chapter 11 hits.
- Hero of Another Story: While Savior's major plot involving 7 friends with different-colored souls, a time-turner, a time machine, and a flower is happening, the Sirius canon plot is happening in the background, coming into the foreground during Azkaban's canon climax, where Frisk tries to run the potion to Lupin in time. Happening somewhat less over time, as now that the Undertale side of the plot is mostly resolved with both Chara and Asriel back thanks to Sans' time machine, the Harry Potter side is coming into the forefront.
- Possibilities story also has this. While Frisk is running around with Opal, Steven, etc. , the rest of the main story happens in the background, with some things brought into the foreground like the Tri-Wizard tournament. A new plot point added in was the puzzle Alphys recommends for inter-class relations, and our main cast trying to figure out the multiple puzzles. Other things are explicitly left out for Logical, Canon, and / or clarification purposes, such as the Yule ball, and other places it wouldn't make sense for Frisk to be in.
- I Am Big Boned: Sans. He is just bones.
- Interclass Friendship: Frisk's friendships with Opal and Steven, a Hufflepuff and Slytherin, respectively.
- Kill It with Fire: Frisk's custom wand can effectively do this with ease, thanks to having a core of Toriel's fur.
- Lightning Glare: Pretty much everyone in the vicinity whenever Sans deploys his "Whoopie Cushion in the hand" trick.
- MacGuffin: Gaster's hand constructs. Sans and Kurt are gathering up the 4 of them because Sans thinks that his soul went into them as they were scattered into different timelines, and can be brought to him to bring him back.
- Mythology Gag: Subtle, but the Stick being made into Frisk's wand is a minor nod to how you could wave it and pretend to be a wizard to spare Madjick.
- In Frisk's first year final, Prof. Flitwick comments that a relative of his was in a "Star Wars Film". Warwick Davis played both Flitwick and Wicket in Return of the Jedi.
- When the Dreemurrs and Oxtobys have dinner together in the new Grillby's in Possibilities, a wizard band plays a song dedicated to the Dreemurrs called "Hopes and Dreams". Both Frisk and Asriel swear they've heard it before, but don't remember where.
- The first time Frisk roleplays talking to Ron with Hermione, Frisk says "Obviously, let's roleplay." which is similar to one of the dialogue options to initiate roleplaying with Alphys on the "date."
- Original Character: Frisk's friends from first year, Opal Oxtoby and Steven Marsh, are both new.
- Parental Abandonment: What truely happens with Frisk and Chara's parents. Chara's parents were Malfoys and Death Eaters, using the Imperius on Chara to make her jump down the hole in Mt. Ebott to avoid risking Chara being raised by "Blood-traitor scum", and Frisk has no idea who her parents were, but they left her anyways.
- Reality Ensues: In Chapter 6, oh so much. The boggart turns into Frisk's worst fear: being unable to save Asriel.
- Roaring Rampage of Revenge: Not quite roaring, but after seeing muggle children being held in the air during the World Cup attack, Asgore and Toriel immediately leap into action against the Death Eaters.
- Running Gag: Roleplaying. Twice, Hermione wants Frisk's help with figuring out what to say to Ron or Harry, and twice, they roleplayed it. When Cedric helps Opal apologize to Frisk, she wonders if they roleplayed it first.
- Shared Universe
- Shout-Out: Several. Steven references both Winston Churchill and Batman of all people, to be the ones he looks up to. The protagonists even get into a friendly discussion over what house Batman would be in. Ron is tellingly confused.
- One of Frisk's classmates has a boggart that turns into Nightmare Bonny.
- This may become a plot point later, when Frisk uses Monster Soul magic on Sirius Black and Peter Pettigrew, it notes both a soul of conflicting Black and Yellow, and a soul of Pink, most likely referencing Glitchtale's use of Black as Hate, and Pink as Fear.
- Quite literally in the newest chapter of "Possibilities", Sans and Kurt travel to another timeline that references Universetale
- Would Hurt a Child: Cormac McLaggen. Intentionally tries harming a first year just because he was in Slytherin. If Frisk had not stepped in, Steven would probably have a fractured leg. Ouch. The fic explicitly states that Frisk's soul was damaged because Cormac had the intent to hurt.
- You Are Better Than You Think You Are: Chara is deeply scarred by her past as a Malfoy and repeatedly says that she "isn't that person" and "can never be that person again". Dumbledore tells her that she doesn't have to be, but should also come to terms with who she was; Toriel also tells Chara that to her, she will always be Chara Dreemurr.
- You Shouldn't Know This Already: Professor Lupin is very concerned when Frisk knows exactly what happens to someone who is soul-less.