No DOG dies, a cat does, and there is a different space for that on this list.

near the end of s1ep5 there's a dying deer crying out it seems it was hit by a car and left to agonize, they were gonna shoot it to put the poor thing out of its misery but something quickly snatches it away, it's obviously computerized but still realist and painful to watch. Highkey upset that no one mentioned this before and that I had to see it myself

Before the rats explode, they are seen and heard in extreme pain and writhing around.

No horses are seen, as far as I know. There is a deer that is seen injured, however, and it is grabbed by a creature. We later see the creature eating something, which is presumably the deer.

In episode 4 season 2 it shows a cat being eaten

bugs and the like are not really shown in the season 2 but the upside down contains snake-like vines

Not a dragon but a monster.

no actual spiders but the mindflayer has a very spider-like shape at some points so just be careful with yourself

Hopper is shown abusing alcohol and has a history of abusing the drug Tuinal (depicted in previous seasons but not this one).

There's an allusion to Hopper's former drug addiction. S3E6 involves two characters being injected with drugs while captured. They end up vomiting in a bathroom but are ultimately fine.

A boys father is an alcoholic, and it’s hinted at that one of the characters is as well

S3E8: There is a close-up shot of a character's leg being sliced open with a knife.

Two young adults are held captive and tortured in an attempt to get information out of them.

A monster is burnt alive, but does not die.

There's no cannibalism in the sense of eating members of the same species, but some monsters eat people.

Brains are exploded. The head(s) remains in tact.

broken teeth are seen when a villain's face is bashed in

A boy becomes possessed by a supernatural being. When a part of this supernatural being is burnt with a flamethrower, the boy is thrown onto the ground and starts to have a seizure.

Steve is beaten and sustains some facial injuries. He develops a nasty black eye, and his eyeballs end up pretty bloodshot. His eyes are never stabbed, etc.

Steve almost has his fingernail pulled out by a Russian doctor.

Eleven breaks a kids arm in season one, because he was bullying Mike and Dustin. It is not that graphic, he just screams Ah! She broke my arm! Let's get out of here!"

A character named Bob who's introduced in the second season dies in episode 8 of the same season. He was dating Joyce, so he acted as a pseudo-father for Will and Jonathon. The death is graphically shown on screen.

the russian base sequence might be a bit much if you have trouble with kidnapping/being caught and trapped

Barbara is a teenager, who is killed and harvested by the Demogorgan

She thinks about it, but backs out.

season 3, at the fourth of july fair

I don't quite remember what episode but there was a part where Billy and Steve were talking while taking a shower at the school.

A character happens upon a pool party and takes some voyeuristic photos of other characters at the party.

The deer scene is definitely a jumpscare.

No ghosts of the dead, but a kid is possessed by another living entity in season 2

This is a major theme in season two and even more in season three.

The most notable instance of audio gore I can think of is when Eleven's leg is injured in Season 3.

At the end of season 1 in the basement Lucas sings a tune about how Dustin farted

In one of the last episodes, Steve and Robin throw up into movie theatre toilets after being drugged.

Not a mental institution, but a schizophrenic person is taken by ambulance and hospitalized

El’s mother is shown to have been tortured with electro-therapy to the point of being permanently catatonic

multiple times throughout the three seasons

Near the end of season 2 a needle is jammed into the neck of a character in self defense. The character is knocked out but does not die.

I would add to the other comment that in the final episode, a child is shown, via flashbacks, in the final stages of cancer and going into cardiac arrest in the hospital.

Season one a kid's mother keeps being told she is crazy by the community, and in season three, a woman is repeatedly told she's imagining things by the men at her workplace and her boyfriend

Eleven appears to be having anxiety attacks several times after she rips off her blindfold

in s1 episode two eleven is show being put in a confined space and crying, and also in a closet. i feel like those count...

SPOILER a character takes their own life in order to save the world in the last episode

A few characters in season one cut, but not for self harm. They are using blood to attract a creature

literally almost every episode

in episode 2 billy has a fairly lengthy scene with shakey cam

There is childbirth in season 2

Terry Ives (A.K.A Eleven's mother), introduced mostly in season 2, is told to have had a miscarriage, when really they stole Eleven/Jane from her because of Eleven's mind powers.

She doesn't die, but does end up being permanently catatonic sometime after she has had her baby.

While no one is outright sexually assaulted, there is a scene near the end of episode 2 which greatly resembles sexual assault, using common stock phrases used in sexual assault scenes. People who are triggered by this may be just as bothered by this imagery

Mild references to sexual content

sorta, initially eleven is thought to be a boy by several people. it's never malicious though

While Robin, who is revealed late in season 3 to be a lesbian, is seriously imperiled and tortured/drugged, she survives and recovers.

billy's dad calls him a f*ggot. there are also racist implications in his actions; he tries to keep max away from lucas, and no reason is given other than the implication that it's because he's dark-skinned. (props to the brothers for making a realistic central indiana from the 80's, i guess.) not to mention that in the very first episode, the bullies make fun of lucas's race by calling him midnight.

Episode 1 Season 3 around 19 minutes, the lifeguard yells and calls a kid lard ass

there are multiple uses of the ableist slur "ps*cho", and ableism towards a woman alleged to be schizophrenic

There aren’t any n-words but there is racial conflict which results in a white character attacking a black character.

Only one usage of the f-slur, from what I can remember.

S2:E1 Hopper claims a story is fake by comparing it to the story about 'the fat man with the beard who climbs down chimneys'

Each season stands alone to some degree. The first season is mostly happy, though bittersweet due to the loss of a character. The Second season ends on a very much happy ending, though teases more to come

S3E6: a brief memory around minute 49. A husband is shown yelling at his wife accusing her of cheating. The wife throws plates, and a child tries to intervene. The husband is verbally abusive toward the wife, pushes the child out of the way, and punches his wife in the face. These same memories are shown quickly in the middle of S3E8.

Technically. Eleven uses her powers to lift a parked vehicle into the air and throw it at several enemies.

S3E6: a brief memory around minute 49 of a father being verbally abusive and pushing his son out of the way in order to hit his wife. These same memories are shown quickly in the middle of S3E8.

in season one, mike nearly falls to his death, but is saved by eleven. i feel this should still be mentioned, since it's a very scary, suspenseful scene.

S3E3: A character is shown gasping for air after her head shoots up from a bathtub. S3E6: The character in the bathtub is shown again. A character is thrown back onto the beach by a wave and coughs out water.

S3E7: A minor character is shot and dies. A human antagonist is shot several times but is revealed to be wearing a bulletproof vest.

The main monster of season 3 is almost literally made out of gore. Also, several rats and humans explode. It’s extremely nasty

First episode, Billy crashes his car while on his way to the motel. I believe seventh episode Eleven throws a car towards Russians about to attack the gang. Finally, the scoops troop slams into Billy’s car while he’s about to run into Nancy and the rest in the car.