There are dead birds and whales.

The scene in which a dog dies happens as the result of player choices, and not all players will see it. However, it is not obvious which choices will lead to this outcome. Discretion advised.

Multiple birds through out the series

It's mentioned that one character rescued his dog from a dog fighting ring, but there's no dog fighting in the game

In the episode Farewell of Before the Storm, which takes place several years before the main story, a character's pet cat passed away before the episode took place. It's not dwelled upon too much, but you do have the option to place a flower at the cat's grave, which will be noted by the characters if you choose to do so.

Butterflies play a big role in this game

Several characters use drugs, although the most you see actually used on screen is pot. One character is a drug dealer, and a major puzzle involves using the drug dealer's list of customer contacts in order to find a culprit. Most, if not all the contacts are underage. Some of the drugs sold are hard drugs too. Additionally, the main antagonist drugs their victims so that they lie prone for their disturbing art pieces.

The father of one of the main characters passed away in a car accident prior to the events of the game. This was a major turning point for said character's life, so it's brought up fairly frequently.

The main character is kidnapped in the final episode, and many other characters have been kidnapped before that as well.

In one ending, the entire town dies which includes a 16 year old boy, and obviously more unmentioned children.

A minor character gets cheated on with her boyfriend and was tricked into thinking her friend was involved

There is a short shower scene that doesn't show any nudity and is non sexual.

In the prequel game, a boy stalks the main character and follows her to her love interest's home. This character is incredibly obsessive over her throughout the game.

A semi-transparent deer seen several times is strongly implied to be the ghostly presence of a deceased character.

A girl vomits after digging up a dead body.

Depending on various choices, you may visit a character in a hospital. She is being treated for depression and attempted suicide. It doesn't specify it's a mental hospital.

In the first game, a friend of the main character goes to the hospital after a failed suicide attempt (depending on the player's choice) and the main character visits her in the hospital. In the prequel game, the main characters love interest/best friend (depending on the player's choice) in the hospital after she is stabbed. This scene will happen regardless of player choice.

A man administers drugs to tends using syringes

Max has frequent opportunities to get private information about people through conversations or looking through their things, then has the option to rewind time and use this private information to get those people to trust her.

The pills mentioned above are an antidepressant (iirc fluoxetine) which, yes, is used to treat bulimia, but also commonly used to treat anxiety and depression. Since there's no other indication for an ED, it's far more likely the AD was prescribed for the latter.

Episode 2 culminates in a character attempting suicide. You intervene, and depending on what you choose, they can live or die. If they live, they recover and you visit them in a later episode, and get well cards are placed outside their dorm room, but if they die, then they remain dead for the rest of the game [it cannot be reversed like other near death experiences in the game] and it will be mentioned frequently by the characters and story. There will also be a memorial set up by the dorm room. Late in the game, you also have the option to assist a disabled character's suicide, as well.

There’s a flashing light at the Vortex Club party. It doesn’t stop while you’re there.

If Max looks at the home pregnancy test in Dana's room, then rewinds and doesn't touch it, only brings it up, Dana tells Max that she was pregnant, and strongly implies that she got an abortion previously. Nothing happens on screen, and Max can find a doctor's note which shows a previous appointment at a women's health clinic where she most likely got the abortion.

Several characters are said to have sex and it's brought up pretty often, but it all happens off screen. There's a plot point that involves a man taking photos of young girls in slightly sexually provocative poses against their will.

Depending on your final decision, yes. Another character that was implied to be LGBT+ in the main game [and more or less confirmed to be in the prequel game depending on how you play it] has died by the time that the main story has started.

One villain uses slurs against lesbians

There is a lot of ableism directed towards mentally ill characters, and the word 'psycho'/'psychotic' is used in a derogatory manner a ton.

One villain uses slurs against lesbians

There are two possible endings, and both are pretty big downers. One is slightly better than the other, but not by much.

A dog can be hit by a car depending on a choice (I didn't make that choice so I'm not 100% certain of this)

a 19 year old is slapped by her stepfather during an argument

In episode 2, a character can commit suicide by jumping from a rooftop, however it's avoidable.

After the opening credits of episode 1, a character reveals a gun and shoots another character in a school bathroom.

max will sometimes get a nosebleed when she has to time travel; blood due to gun violence is frequently shown, especially at the start of the game when a character is shot and a wound forms

The car crash is a major plot point. The player deals with the aftermath of the crash, and especially the emotional trauma, at great length.