
Summary
Monsters are one of the races which rules over the Earth alongside Humans in Undertale.[1] Unlike the latter, whose SOULs are independent from their body, and thus can persist after death, the Monsters' SOULs are much weaker given that they're linked to their body, thus when they die their SOUL disappears as well, with the exception of the Boss Monsters, whose SOUL can last a bit more after their death. However, despite this difference, Monsters were still feared by the Human race. This was due to a Monster being capable of taking a Human's SOUL after their death, becoming a beast with with unfathomable power. Because of this power the Monsters had, the Humans made a war against them; yet there was a crushing victory due to the difference of power between the SOULs of the races, with the Humans later sealing the surviving Monsters in the Underground with a Spell which created a barrier that prevented them to get out without the Human SOULs.[2]
Monsters are in multiple shapes, ranging from being skeletons like Sans or Papyrus, to being similar to animals like Alphys or Toriel.
General Monster Abilities

Monsters have all the same general abilities as the fundamental parts of their physiology, which are the following:
- Magic, Inorganic Physiology (Type 1) and Danmaku: Monsters' bodies, compared to human ones, do not have much physical matter because of them being made of magic to the same degree humans are made of water, being able to use their magic in various ways like making bullet patterns, which are showcased in most of their fights, with them also being able to control said magic.
- Non-Physical Interaction: Monsters' magic is showcased to be able to actually harm Mad Dummy, who couldn't be damaged from Frisk because of their true body being incorporeal, thus immune to their attacks due to humans lacking magic on their own.
- SOUL Manipulation: Monsters' magic attacks the SOUL, which is the essence of one's being. Some monsters can also manipulate the SOUL of their opponent though inflicting status effects, such as making it heavier or unable to walk away from a point in the area.
- SOUL Absorption, Transformation and Extrasensory Perception: Monsters can absorb the SOUL of a defeated human, transforming in an "horrible beast of unfathomable power", with their power greatly increasing the more SOULs they absorb, as a monster with 7 Human SOULs is described as being a god who can destroy the barrier. They can also feel both the emotions and hearts of the SOULs inside of them.
- Creation: Monsters' magic can create real objects which are tangible.
- Longevity: Monsters' lifespan is implied be of at least thousands of years. Examples are Gerson, who is still alive after participating in the war between humans and monsters, whose result has left the latter imprisoned in the underground for millenia, or the Dogi, who went second in the Nose-Nuzzle comptetition of the '98 against Asgore and Toriel, with said competition happening before Toriel's self-isolation in the ruins, which happened after Chara's fall in the Underground in 201X[3] and lasted[4] likely 100 years.
- Limited Durability Negation: Monsters' magic attacks the SOUL, but is still affected by conventional durability.
Monsters generally have also showcased Resistance to the following abilities:
- Necromancy: As the body of a monster is made of magic, it is attuned to their SOUL. Because of this, they do not leave a corpse at their death, instead turning[5] to dust and with their SOULs also not lasting after dying, but just disappear.
- SOUL Manipulation: As the body of the monsters is made of magic and directly linked to their SOUL, they should be able to take SOUL attacks as physical ones.
- Radiation Manipulation: The Gamerblood Energy Drink is a common product in the Underground despite it containing radioactive waste.
- Possibly to Poison Manipulation: Monsters can stay indefinitely at the CORE, which is seemingly filled of ozone.
Special types of Monsters

The Amalgamates are a whole new type of monsters which was accidentally created from Alphys during her research on the SOULs, as after the war between humans and monsters, she has injected DETERMINATION in the bodies of the dying monsters in an attempt to give them the same power humans had, but with said experiment ending as a failure given that the monsters' bodies lack enough physical matter to sustain it, thus they began to melt and mix into each other, thus creating an amalgamation of monsters.[6]
Other than having the general abilities and resistances all the monsters have, this kind of monsters also has:
- Invulnerability, Healing and Enhanced Absorption: Amalgamates do not have a stable body due to it being unable to sustain DETERMINATION, making them not solid and able to absorb[7] other beings within themselves. They have also shown to absorb damage, with their HP bar increasing instead of decreasing when hit.
- Multiple Selves (Types 2 & 3): The Amalgamates are made of multiple monsters fused[7] in one, with their minds being merged together.
- Supernatural Willpower, Empowerment, Regeneration (High-Mid) and Immortality (Types 3 & Limited 2): Should be the same as Undyne due to her being a monster with DETERMINATION. Amalgamates showcased the ability to reform themselves even after splitting in tiny pieces.
- Shapeshifting and Density Manipulation: As their bodies are not solid, they can take the form of any kind of object through changing both their appearance and weight, whenever is solid or liquid, being unrecognizable from the real ones until being interacted with, even if they take the shape of non-physical objects such as SAVE points or text boxes.

Ghosts are a peculiar type of monsters[8] who, while uncommon, are still notable enough due to them being extremely different than the normal ones. They lack a corporeal form, and because of this they're usually depressed as that prevents them from joining the other monsters in the fun activities they do or to fulfill their own dreams, making them search for a physical body and fully merge with it.
Other than having the general abilities and resistances all the monsters have, this kind of monsters also has:
- Incorporeality: Ghosts are incorporeal, thus being capable to pass through doors, with Frisk's attacks also not having an effect against a ghost due to their lack of magic, as furthermore showcased from their inability to bite a ghost sandwich, instead phasing through it when attempting to do so.
- Immortality (Type 6), Limited Possession and Fusionism: Ghosts can take on an inanimated object, making it their vessel and slowly merging with it until they become fully corporeal, though said process can be vastly accelerated if they are feeling an exceptionally strong emotion.
- Flight: Unlike most of the monsters, ghosts are able to fly.
- Telekinesis: Ghosts can physically interact with objects or even throw them despite lacking limbs.

Boss Monsters are another type of monsters, which is the strongest one.[9] They are different from all the rest, as other than being generally stronger than almost every other monster in the game, Boss Monsters' SOULs can persist after their death after a bit of time before disappearing.[2] The only Boss Monsters which were shown in Undertale are the ones of the Dreemurr family.
Other than having the general abilities and resistances all the monsters have, this kind of monsters also has:
- Immortality (Type 1) and Energy Manipulation: A Boss Monster ages only if they give SOUL power to their biological child to make them grow, with Asgore and Toriel having stopped aging after the death[5] of their biological son.
- Danmaku, Fire Manipulation and Temperature Manipulation: All of the Boss Monsters can use fireballs as bullets for the pattern of their attacks, while also being able to control its temperature. The temperature of these attacks is also high enough to harm Frisk, despite them being unfazed from an overheat explosion from a MTT brand oven, which can reach temperatures of 9000 °F.
- Resistance to Extreme Heat and Extreme Cold: The Underground has places with extreme temperatures, those being Hotland, which is hot enough to vaporize a styrofoam cup and water instantly, and Snowdin, which has ice and snow that are so cold that they resist the temperatures of Hotland, with Undyne finding Snowdin to be significantly cold and spiders even dying there because of this.[4] Boss Monsters such as Asgore are implied to survive in these places despite such temperatures, as he is also[10] Santa Claus, who is well known in the Underground and gives presents across all of it. Due to being the strongest type of monster, they should also be at least the same as Undyne.
Weaknesses
- A monster's body will have its defenses weakened if they refuse to fight against the opponent, and will get even more vulnerable if said opponent has an extreme desire to kill, though a monster who can control DETERMINATION like Undyne the Undying is seemingly able to reduce the effects of said weakness to strong murder intent, as unlike her regular self, she was able to give an actual fight against Frisk in the Genocide Route.
- Same as the other monsters, but including the fact that if they fully merge with a body, they stop being a ghost, thus losing their Incorporeality and almost all the other powers they had as a such, making regular physical attacks able to harm and kill them.
References
- ↑ Undertale Intro
- ↑ 2.0 2.1 Waterfall: The War of Humans and Monsters
- ↑ New Home (Genocide Route)
- ↑ 4.0 4.1 Muffet Battle (Neutral/Pacifist Route)
- ↑ 5.0 5.1 New Home: Asriel's Story (Neutral/Pacifist Route)
- ↑ True Lab
- ↑ 7.0 7.1 True Lab: Entry 17
- ↑ "This monster doesn't seem to have a sense of humor..." -Napstablook's CHECK description
- ↑ Gerson's Dialogue (Post-True Pacifist)
- ↑ UNDERTALE - 5th Anniversary Alarm Clock Winter Dialogue (Asgore)
Discussions
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