Shadow is a shapeshifting monster who feeds off emotions. He is neither good nor evil, though will go to chaotic lengths to achieve his goal (That is, staying alive).
In his base form, Shadow is very bland. He resembles a small, black cloud with no distinguishing features, no mouth, no nose, nothing. When he's about to morph, his cloud-body turns into that of a strange, black liquid that does not give off reflections, he can move surprisingly quickly in this form, though only holds it for seconds at a time. It's also possible for Shadow to seep into the ground, leaving a dark patch as the only indication that he's even there, but he can only do this if he's copied someone and is at least at 50% of his full power.
Shadow's main ability is the fact that he can transform into other people, fooling both them and others on who is the real one. His imitations are not at all perfect, though they usually get the job done just fine (Which is mostly trying to break his target mentally, which he can do through many ways). He has various stages of transformation, with more time giving him a higher percentage of his real power, the stages are as follows:
The weakest of all. Shadow only copies his target's physical form, but not including any weapons they may have on them. He doesn't even copy their voice in this form, and yellow eyes show through where the original person's usually did. This form is very flawed, and Shadow only reaches it if he's given barely any time to copy his target, not recommended.
More powerful than the 10%, Shadow's second transformation is the one he usually adopts. This form copies everything the first form did, along with some weapons of the target, and also their voice (Which is layered on top of Shadow's own). He can take some memories from his target in this form, but usually not enough to hurt them in any way. Finally, this is the first form where he can use his shadow-y powers (Seeping into the ground, "dark leeches", and a lot of other edgy names for stuff). This form still retains the yellow eyes from the 10% form, and also has a slightly darker skin tone than Shadow's target.
The penultimate of Shadow's transformations. It has everything the 50% form had, but more. He copies his target's voice perfectly, copies everything on their body (Weapons, armor, etc), and increases the power of his own abilities. He can copy all their memories, and can even form a mind-link with his target, so every thought they have, he has too (Though, vice versa also applies). In this form, Shadow can choose to keep his yellow eyes and slightly darker skin, or he can copy his target completely, whichever he chooses.
Shadow's final transformation, and the most powerful of all. He can only achieve this form if the target agrees to give him their SOUL, which he always offers to take before fighting them. Upon taking their SOUL, Shadow will transform into them perfectly, copying their mannerisms, speech patterns, simply everything about them. This form is only slightly more powerful than his 100% transformation, though that shouldn't matter much, as he can fight the same way the target does anyway. The best part of this transformation comes from one single fact: For Shadow, absorbing a SOUL doesn't increase his power by anything, instead, he can return to that form whenever he chooses, even if he never sees the body of the person he's copied. With all this in mind, Shadow has only ever achieved this form once, and it's rather unlikely he'll ever be able to do so again.
Shadow's real personality is not often shown, he's usually busy copying someone else's. On the rare occasion that he does show hints of his true personality, it's revealed that he is a tad reckless, doesn't care for anyone or his surroundings. That being said, he does enjoy making fun of people, their sadness, anger and/or laughter causes him both entertainment and energy.
Shadow is generally a loner, he grows tired of people quickly. While at times he does wish he could have a few people to depend on, he realises it would only cause both him and them pain when the eventual time comes when he would have had to copy them. Other than that, though, Shadow enjoys long metaphorical walks along Hotland's metaphorical beach, which gives him time to be alone and relax.
The only thing he truly fears are the Amalgamates, which he learned about after copying Alphys once. While they technically have more than one SOUL, he believes that if he copies them, he'll become just as mindless and broken as they are, which he does not want. As a tradeoff, the Amalgamates give off a very large amount of emotional energy, so if he can brave them for just a while, Shadow could get a large boost in lifespan.
Shadow's backstory is one not known to many people but himself. He wasn't always a cloud shapeshifter, in fact, long ago, he was a normal monster. As all things do, Shadow died, and his body turned to dust. Time seemed to stop for him as someone appeared... A human with a kind demeanour. Shadow couldn't tell exactly who they were, but they offered him something. In exchange for keeping tabs on him for a while, so they would know what came of it, they offered Shadow immortality.
Shadow agreed without a second thought, and so the deal was done. Because his original body had disappeared, Shadow was left with a replacement: a cloud-like body, with the ability to fly. But this wasn't the best part, that title belonged to the fact that Shadow could replicate any body he wished from anyone, provided he had seen them in person, and that they did not have any more or any less than one SOUL.
Shadow roams around the Underground and looks for anyone who might be a good source of emotional energy. If he finds one, he copies them, and he lives on.
Fighting Shadow is a very different battle than any other normal enemy. First, Shadow fights the Player in his own form, but soon copies them for extra power. After that, he delves into their memories and takes the form of Toriel- and if the player befriended him, Papyrus. He uses the attacks of the latter two when he turns into them, and uses unique attacks when taking the form of the Player, both of which depending on whether they've killed anyone or not.
Shadow launches homing white bullets in on the Player, in an attack similar to Flowey's. He always does this on the first turn, before copying them on his second.
Shadow mimics the player's current weapon and unleashes a different attack based on whatever weapon they use. If they're using any sort of Knife or the stick, they must dodge one fast moving projectile. If they're using the Burnt Pan or Torn Notebook, a slow moving, yet very large pan will need to be dodged. If they're using the Ballet Shoes or Tough Glove, lots of small projectiles will need to be dodged. Finally, if the player is using the Empty Gun, Shadow will simply throw it away and attack them with the same move he did as his first attack.
On the third turn, Shadow will mimic Toriel's attacks. He will use all the attacks she used until he either gets to low enough health or until the player uses specific ACTs.
Finally, he will mimic Papyrus, if the player befriended him (If not, the battle will end after he finishes copying Toriel). He will launch all kinds of bone attacks at the player, and even briefly give them the Blue SOUL.
Check, Compliment, Talk, Hug
To spare Shadow, he must be Talked to until he assumes the form of Papyrus. In which case, he must then be Talked to again once, and then Hugged. Complimenting can also work as an alternative to Hug.
If Papyrus was not befriended, or was killed, Shadow will end the battle as Toriel. The player must talk to him once in that form, and then hug him. If the player flirted with Toriel, Compliment can also be used.
*A cloud appears...? -Encounter
*You'll Face Yourself. -Neutral, assuming the Player's form
*Toriel blocks the way?! -Assuming Toriel's form, first turn
*Toriel looks through you... But something's different. -Neutral, assuming Toriel's form
*Toriel prepares a magical attack... But something's different. -Neutral, assuming
*Papyrus blocks the way?! -Assuming Papyrus' form, first turn
*You're blue again. -After Shadow Papyrus' Blue Attack
*Smells like shady bones. -Neutral
*Papyrus whispers "Heh nyeh nyeh!" -Neutral
*??? ??? ATK ??? DEF. Looks like your friends, but it can't be... -Check
*You deliver a compliment to the cloud/yourself/Toriel/Papyrus... They're flattered. DEF down. -Compliment, before spare conditions
*You strike up a conversation about the weather... But they're not listening! -Talk #1
*You ask why they're attacking you... You see a glint of remorse in their eyes. -Talk #2
- You ask them to stop, they shake their head. -Talk #3
*You tell them you don't want to fight. They look angry... -Talk #4
*You tell them thourougly to STOP fighting. They deeply sigh. -Talk #5
*You tell them nobody needs to die. They let their guard down. -Talk #6
*You wrapped your arms around them... They did the same. -Hug, spare conditions met
*You tried to hug them... But they pushed you away! -Hug, before spare conditions
*You tell Papyrus/Toriel he/she's looking awfully nice. -Compliment, spare conditions met
*Looks like you ended this peacefully. -Spareable
"..." -Before battle, Talk in battle, Compliment in battle, Hug in battle.
"You're a Human. My name is Shadow. It might be best if we never talk again." -Post-battle
HP - 100
ATK - 0
DEF - 0
In his base form, Shadow cannot attack and has basically no defense since he's a cloud. When he mimics someone, he can copy their stats instead at 50% and up. For his 10% transformation, he gains 5 ATK and DEF and 500 HP.
- Shadow's name, transformation ability and the golden eyes from said ability are based on the Shadow Selves from the Persona series.
- Before he died, Shadow's favourite thing to do was drink chocolate milk. In his new form, he can't do that. Whether this is why he doesn't care about anything anymore is unknown.