Top 5 Controversial Decisions in Undertale

If you want to see friendships tested and group chats explode, just ask an “Undertale” fan about the most controversial decisions Toby Fox made in that game. “Undertale” isn’t just a pixel-art RPG—it’s a phenomenon with a fandom known for passionate, and sometimes heated, debate. Today, I’m counting down the top five most controversial creator decisions in “Undertale” history. Each one of these has divided fans, inspired essays, and sparked flame wars that still haven’t burned out. Get ready—this ranking will absolutely get the comments section fighting.

Number 5: The Multiple Endings and Morality System

Toby Fox designed “Undertale” so your choices shape the world, the characters, and—most famously—how the story ends. You can complete the game never killing anyone, following the Pacifist route, or you can kill every monster you meet, taking the Genocide path, with a Neutral ending lying somewhere in between. While the branching story was praised for its depth, these choices set off a firestorm among players. Some fans argued the game “punishes” Genocide players too harshly, locking out future true Pacifist endings unless you delete your save data. Others felt the Pacifist ending was too forgiving, letting players “reset” and erase their mistakes. The debate boils down to whether a game should give players freedom with consequences, or allow all actions to be redeemed without long-term impact. This morality system is still dissected in forums and YouTube essays years after release.

Number 4: The True Lab and Amalgamates

Halfway through the Pacifist route, players enter the True Lab—a hidden research facility beneath Alphys’s lab. Here, they discover the Amalgamates, disturbing fusions of monsters created through failed experiments. These monsters are a sharp tonal shift from the witty, upbeat vibe of the rest of the game, delving into body horror and tragic backstory territory. Fans were split: some admired the darker lore and how it gave Alphys complex motivations, while others found it tonally jarring and emotionally manipulative. There are heated debates over whether the Amalgamates’ presence deepens the game or undercuts its charm. Some players even avoid the True Lab altogether on replays, not wanting to revisit its unsettling atmosphere.

Number 3: The Fourth Wall Breaks and “Dog Residue”

Toby Fox is notorious for breaking the fourth wall in “Undertale.” One of the most infamous examples is the recurring “Dog Residue” item, which can fill your inventory endlessly if you keep using it, making it both a money exploit and a running gag. The game also features meta moments where characters address the player directly, or even remember if you’ve “reset” the timeline. Some fans love these meta touches, arguing it’s what makes “Undertale” unique and self-aware. Others feel it disrupts immersion and punishes players for experimenting, especially in the Genocide route when characters like Sans seem to accuse the player personally. The intensity of these fourth wall breaks has led to arguments about whether they’re clever or condescending, and if they enhance or undermine the story.

Number 2: The Characterization of Flowey

Flowey, the game’s first “villain,” is a sentient, malevolent flower with the ability to manipulate time and memory. He taunts and attacks the player, but later is revealed to be Asriel Dreemurr, a tragic figure caught between innocence and nihilism. Toby Fox’s decision to give Flowey such a complex, morally ambiguous role has divided the fandom for years. Some see Flowey as a masterstroke—a villain whose cruelty is rooted in loss and emptiness, making his story arc deeply moving. Others feel that Flowey’s redemption comes too late, or that his actions are too unforgivable for any amount of backstory to justify. Arguments rage over whether Flowey’s transformation was earned, and if his ultimate fate should have been left to the player’s choice. The character inspires fan works, but also constant debate over the line between villainy and victimhood.

Number 1: Sans’s Impossible Boss Fight on the Genocide Route

At the very top of the list is the infamously brutal Sans boss fight, only available if you choose the Genocide route and kill every monster in the Underground. This fight is legendary for its difficulty. Sans’s attacks ignore the game’s usual rules—he hits you with poison damage, dodges attacks, and breaks the game’s fourth wall with dialogue and mechanics. Many players spent dozens, even hundreds, of attempts trying to defeat him. This decision by Toby Fox—to make the game punishingly hard for players who chose the “evil” route—sparked one of the fiercest debates in the fandom. Some argue it’s a perfect narrative consequence, making you “earn” your villainy with sweat and struggle. Others think it’s unfair, calling it a form of shaming or “player harassment,” especially since the Genocide route is already bleak and emotionally taxing. The difficulty of Sans’s fight, and the way the game treats Genocide players, has become the most hotly contested subject in Undertale’s history. For many, it’s the ultimate test of skill and narrative conviction; for others, it’s a punishing wall that says “you’re not welcome here.”

And there you have it: the five decisions by Toby Fox that split the Undertale fandom down the middle. Maybe your personal most controversial moment didn’t even make the cut. Did we rank them right? Did we forget your favorite hot take? Let us know—because in the Underground, the debate never ends.