Undertale: The RPG That Remembers What You Did

Toby Fox released Undertale in September 2015, built largely alone over three years with music, writing and design all coming from the same person, and the thing that made it stick was never the jokes, good as they are. It was the combat screen. Every RPG since Dragon Quest has treated a battle menu as a set of verbs for winning: Attack, Magic, Item, Run. Undertale keeps that menu and adds one word — Mercy — that quietly reorganises what the other three mean. Once Mercy is on the list, Attack stops being the default. It becomes a choice you have to keep making, and the game keeps a ledger of every time you make it.

The bullet hell is a conversation

Encounters in Undertale run on two screens stitched together. The top is dialogue with a monster; the bottom drops you into a bullet-hell box where you dodge attacks with a small red heart. That pairing is the whole trick. The bullet patterns are each monster’s personality rendered as a wave function, never neutral obstacle courses. Toriel’s fireballs arc wide and give you room to escape unhurt, because she does not want to hurt you. Papyrus’s attacks are absurd, telegraphed, gentle, because Papyrus does not actually want a fight, he wants a friend. Undyne’s patterns tighten and speed up the longer you refuse to strike back, because Undyne is furious that mercy is even on the table when her friends are getting hurt. You “win” most of these encounters by reading a personality until you know which action — compliment, flirt, cower, spare — resolves the standoff, rather than by exhausting a health bar. The RPG interface survives; the victory condition underneath it has been swapped for something closer to a negotiation.

That swap only works because the bullet hell half is genuinely testing you. If sparing were free, the game would be a visual novel with padding. It isn’t free. You still have to dodge Toriel’s fire and Undyne’s spears competently while you work out how to end things without a corpse, and that friction is what makes the Pacifist route feel earned rather than handed to you. Hades solves a related problem — how do you make a story hold up across dozens of forced repeats — by having its cast comment on the repetition itself. Undertale solves it by making the repetition optional and expensive: grinding levels off monsters you’ve already befriended reads, correctly, as a betrayal the game will not let you take back for free.

The overworld is doing the same job quietly

The turn-based encounters get most of the attention because they’re the mechanically novel part, but the overworld between fights is running a smaller version of the same trick. Snowdin’s puzzles are trivially easy — Papyrus designed most of them, and Papyrus’s traps are exactly as threatening as Papyrus himself, which is to say not at all. Waterfall’s are moodier and stranger, echoing the area’s theme of forgotten things and untold history. None of these puzzles are difficult in the way a genre-standard adventure game’s are; they’re characterisation wearing a puzzle’s clothes, the same disguise the combat menu wears over its negotiation system. A locked door in Undertale almost never tests your reasoning as hard as it tests whether you’ve been paying attention to who built it and why, which is a strange thing for a puzzle to optimise for and exactly the reason the Underground feels inhabited rather than assembled.

The save file is a character

The detail that made Undertale a genuine cultural event rather than a well-reviewed RPG is that its true antagonist is aware you can reload. Flowey, the game’s first creature and its ultimate one, remembers resets that happened on a save file you deleted. He references choices from a playthrough the current file has no record of. The game is being honest about what a save scummer normally gets away with — it is telling you the scumming was observed. Permadeath and the stories it buys usually work by removing the reset button entirely, forcing consequence through scarcity. Undertale takes the opposite route: it leaves the reset button fully functional and then punishes you for having pressed it, which is a harder trick to land honestly, because it requires the game to actually track state outside its own save data — a genocide run leaves scars a from-scratch pacifist file cannot fully scrub, and the game tells you so.

This is where the writing does its heaviest lifting. Sans, the game’s laziest-seeming character, is written to react differently depending on what you’ve done in a run he has no diegetic reason to know about. Played straight, he’s a pun machine leaning on a hot dog stand. Played against a genocide route, he becomes the only creature in the Underground who has correctly clocked what you are, and the fight that follows is less a boss encounter than an accusation with attack patterns. None of that would land if the combat system were purely mechanical. Because Mercy has already trained you to read fights as character moments, the game can spend that trust on a joke character and turn him into the story’s conscience without breaking tone.

The jokes are load-bearing

It is easy to mistake Undertale’s comedy for seasoning on top of the mechanical structure, when it is closer to a delivery system for the same trust the combat menu is building. Sans’s recurring bad puns, Papyrus’s spaghetti obsession, the skeleton brothers’ entire dynamic of one sincere goofball and one aspirational goofball trying to become a Royal Guardsman — none of it reads as filler once you notice how carefully it’s rationed. A joke character gets to be purely a joke for exactly as long as the plot needs comic relief, and the moment the plot needs him to be something else, the game has already spent enough screen time on him that the tonal whiplash lands instead of feeling cheap. Mettaton, introduced as a preening game-show robot running a gauntlet of quiz segments and cooking-show parodies, gets an entire boss fight staged as a live broadcast, complete with a rating meter that goes up if you play along with the theatre of it. The joke is the encounter design. Undyne’s own arc runs the other way: comic bluster escalating into one of the game’s most sincere speeches about found family, delivered by a fish woman who spent her first appearance chasing you through a house made of puzzles.

Muffet’s fight works the same trick from a different angle — a spider extorting “donations” from you mid-battle, whose pattern of falling teacups and cupcakes can be ended early if you actually pay her, which is funny until you realise the game just modelled a boss fight as a shakedown you can resolve with currency instead of violence, one more spare disguised as a punchline. By the time the credits genuinely move you, and for most players they do, it’s because the comedy spent the whole runtime training you not to expect anything else, then cashed that expectation in.

What the routes actually argue

Undertale is frequently summarised as “the game where you can be nice instead,” which undersells what the Pacifist, Neutral and Genocide routes are actually doing structurally. They are not difficulty settings or moral quizzes with a score at the end. They are three different answers to the question an RPG never usually asks out loud: what is a monster, dramatically, if not an XP delivery mechanism? Neutral is what happens if you play an RPG the way RPGs train you to play them — some fights avoided, some not, no particular commitment either way — and the game responds by killing off named characters almost as an accounting exercise, the way a normal RPG’s world would collapse if its logic were taken literally. Genocide requires you to actively hunt down every monster in every area, including ones who flee, which the game makes tedious and slow on purpose; it will not let “the true ending” be an accident of a min-max playthrough.

Pacifist is the hard route, mechanically and emotionally, because sparing something that is actively trying to kill you requires reading it correctly under pressure, in real time, without a menu that tells you the right verb. The reward for getting it right across an entire cast is a final act that recontextualises everything — Asgore, Asriel, the entire premise of a underground kingdom of monsters sealed away by a human war centuries earlier — as a story about grief that a combat system had been quietly building toward the whole time. Toby Fox wrote every arc, scored every arc, and coded the framework that lets Mercy mean something different in each one. Three years, one credited author on most of it, and an RPG combat menu that finally admits the obvious: the numbers were always a proxy for a decision about another creature’s life, and the genre had just never bothered to ask you to notice.

The lineage this actually started

The direct descendants are easy to name — Toby Fox’s own Deltarune reuses the Mercy button and then interrogates it further by removing the ability to kill most enemies at all, forcing the question of what a spare means when violence was never really on the table. But the wider influence runs through every indie RPG since that has tried to make its battle system argue something instead of just gating progress: OMORI’s emotion system, Cassette Beasts’ refusal to let capture be morally free, a dozen smaller RPG Maker games that borrowed the bullet-hell overlay wholesale without always earning it. That last group is instructive by contrast. Bolt a dodging minigame onto dialogue and you get spectacle; pair it with a save file that remembers what the dodging minigame was actually for, the way Undertale does, and you get a combat system that can carry a story’s entire argument on its own syntax. Fox proved the trick works even solo, on a three-year budget, with sprites that would have looked dated on the SNES — proof that the idea was always the expensive part, not the production values wrapped around it.

Spoilers below

The True Pacifist ending resolves the barrier sealing monsters underground only after every named character survives a full playthrough, which is why a single missed spare — Papyrus killed in a previous Neutral attempt, Undyne’s fate mishandled — locks it out entirely; the game checks save data across resets to confirm it, the mechanic Flowey warns you about made literal. Asriel’s reveal as Flowey, and the flower’s backstory as Asriel’s soul without the compassion that made him Asriel, is the payoff the whole Mercy system was built to deliver: a monster who cannot be spared because sparing requires the capacity to be moved, which he traded away first. Genocide’s final fight, against Sans, is deliberately the hardest encounter Toby Fox could design, because it is the only fight where the game wants you to lose, repeatedly, until you understand exactly what you chose to become to get there.