You can choose to kill a variety of dogs in the game, but it is not recommended as the good ending" of the game involves sparing every creature you run into

There is a very difficult-to-find monster encounter which is very dragon-like (and described by his creator as a "butterdragon"). Like other monster encounters, it is possible but not required or recommended to kill him.

There are monster characters resembling other animals - for example, one is a deer - that can be killed.

Various animals can be killed.

In the not good endings, yes. BUT YOU CAN PET THEM INSTEAD OF FIGHT THEM.

Froggit attacks include swarms of flies

A horse-mermaid type monster can by killed by the player ingame, but it is optional and discouraged.

There is a spider monster, Muffet, who bakes with spiders. In her battle, spider's aid her. If you spare her or eat one of her treats, she's friendly to you.

There is a monster encounter where your adversary is a cat-like creature. Like all monster encounters in this game, it is possible (but not required or recommended) to kill her. Additionally, there is an anthropomorphic cat creature who acts as a shopkeeper and cannot be fought. In the worst possible ending, the entire world is destroyed, killing all remaining monsters including the cat shopkeeper.

A monster in the game's short Hard Mode has snakes on its body.

There is a disabled dog named Doggo. He smokes dog biscuits.

There is one NPC in Grillby's known as "Drunk Bun" who could be seen as an alcoholic.

There’s a dog who “smokes dog biscuits,” but this is purely for comedic effect and it’s never listed as addiction.

In the true pacifist route, Undyne's house burns down. The house is shaped like a fish so it comedically shows it; the windows of the house are eyes, so there are flames in it and "tears."

There is one character who wears an eyepatch, and a few monsters are based on eyes. No violence is done to eyes unless you perpetrate it, however.

There is no shaving in undertale lmao

I... I mean... you can kill a skeleton...

The creation of the Amalgamates is assumed to be torture, but they and their families seem to be fine with being mixed with several other people.

When on the "no mercy" path, after killing one boss his head becomes detached from his body while his body is reduced to dust. His head becomes dust separately. This is commonly interpreted (and regularly depicted in fan material) as being the result of the player crushing his head under their foot.

When the playable child character is taken in by a motherly goat creature who intends to keep you as her own. She is disappointed when you leave, but understands that you are not her child. Your character resembles the first human child that this motherly goat creature adopted. So implied kidnapping? Additionally a silly skeleton creature “captures” you after he defeats you in battle. You are put into a room with dog supplies and a fence, but can easily escape through the bars to continue your journey.

Is one of the plot points but is not graphically showed

The parents of Asriel Dreamer, Toriel and Asgore, can be killed by the protagonist. When they are killed, they have slashes across themselves and turn into dust. However it is your choice if they die or not.

A ghost possesses a training dummy but I'm like 99% sure the dummy wasn't sentient before that?

In the short Hard Mode, there is a special monster encounter with a clown face and described as a "messed-up clownbug".

A figure can be seen behind a shower curtain, but pulling it back reveals that nothing was there.

After leaving the Ruins (all routes), a door clicks and Sans' shadow appears behind a tree The elevator to the True Lab (Pacifist route) suddenly falls and a siren plays Neither are exactly scary but they made me jump lmao

Though there is a ghost name Napstablook, he is a comical character and does not attempt to be scary in any way throughout the game

Sometimes you can see Flowey stalking the player.

There are whoopie cushions, however.

Portions of Alphys' lab are reminiscent of a hospital.

Not on-screen, but there are references to injections in the lab notes of one character experimenting on other people.

Yes, someone slowly dies by poisoning themselves in the backstory.

Alphys has problems with anxiety

A monster dog amalgamate approaches you in a narrow hallway. They become placid after several pets.

One character's backstory has strong parallels with dysphoria, but this backstory (found in diaries) is completely optional to read.

There is one successful and two attempted suicides in the backstory. Furthermore, two characters can commit suicide during the game, one implied and the other on-screen (though non-graphic). Both of them survive in the pacifist route.

Tapes found in the TRUE LAB, contain gaslighting.

The elevators shake a little bit but I don't think it's enough to count?

The last fight of a Neutral run and Pacifist run can have strobe effects.

There are multiple LGBT characters who *can* die but they all survive in a pacifist playthrough.

Not in canon, at least.

It really only depends on what route you play, if you do a genocide Route then of cause there’s not a happy ending, there’s a fair amount of what one would call neutral endings though

there is eye gore shown toward the very end of the genocide route. there is another instance of possible blood in the genocide route, but considering the character it happens to, it could just be ketchup.

There are no graphic depictions of child abuse, but there are heavy implications of child abuse in some routes.

There’s multiple people that fall from a large heights, but none of them die

The main character can use an empty gun as a weapon but it isn't really shown as any different than using other weapons. There's also cartoonish guns in one fight

You have the option to kill a plane shaped enemy. Their death animation shows them crashing to the ground. This is more comical than anything and the only fatality is the plane monster.

A visible coffin (sometimes with the bandages left behind) is left open in one room.