- Excalibur dying near the end of the pilot.
- Whatever friendship Cassandra and Jake had in the first episode is thrown out the window the moment she betrayed the team. Several episodes have had her trying get him to trust her again, but he says he won't ever trust her again, even though he like her and enjoys working with her.
- Cassandra's explanation of her tumor in "And the Heart of Darkness". She says she was told about it when she was 15, and she sees death when she looks in the mirror.
- The ending of "And the City of Light": The team thought that they had botched the calculations for Tesla's device, so they try to switch it off, resulting in the lost town's inhabitants being trapped between dimensions for at least a hundred years and Mabel actually dying.
- Just to rub it in, as Stone and Mabel make their way to pull the plug, they trade made-up stories about traveling the world together in a Call-Back to an earlier conversation. The last shot of the episode is Stone stepping out of the Annex onto the streets of Paris, carrying with him all the postcards of the places that Mabel wanted to visit and never got the chance to.
- Lamia's death in the season 1 finale. She may have been evil but being betrayed by Dulaque is pretty cruel worse when later in an Alternate Timeline we are shown that she is capable of being good.
- In "The Drowned Book" Jake is about to do his part of the plan to redirect the library's second sun to a storm in order to stop it. Cassandra is worried and Jake promises that he'd be fine since they were fine when they went their own way, Cassandra replies with this.Cassandra: We weren't fine, we weren't okay. I don't even know why we went our separate ways.
- Stone's strained relationship with his father. The elder Stone is so convinced of his son's uselessness that he refuses to listen to anything Jacob tries to tell him, even belittling him to his colleagues.
Stone: My father would die before he ever told me that.
- The fact that Stone realizes it's the shapeshifter impersonating his father because he told Stone he loved him.
- Cassandra's "truth" that she shared to open the door After the doctors told her that her tumor would kill her, she decided that she would go out on her own terms and has already picked an unknown day in the future to "die on her own terms"
- The death of Stumpy the Gargoyle in "And the Cost of Education".
- Ezekiel points out that everyone in the Library crew is perfectly expendable. He has no real ties to the real world, Stone is alienated from his entire family and has no real friends, and Cassandra has her brain tumor.
- Watching Ezekiel slowly break in "And The Point Of Salvation". Of all the people to watch their friends die over and over, Ezekiel was probably the best choice, but that doesn't make it the easiest one to watch. Not to mention by the last restart, the game is glitching, so no more restarts, and items and enemies are moved so Ezekiel can't point them out to his friends to prove he is telling the truth. You can see the desperation from Ezekiel when he begs for them to put aside their usual expectations of him and to trust him to lead them to safety.
Ezekiel: There's a save point just beyond that door. We've made it to the central stand a couple times, but-Baird: [shocked] Jones!Ezekiel: Maybe if we split up, then we-Baird: Ezekiel. How many times?Ezekiel: [tired] ...I've lost count.
- The sheer amount of Fridge Horror in the episode. If not for the resets, Ezekiel really would have gotten them all killed. He took about 5 tries to open the lock, sixty-ish times running the gate, and he's lost count on going through the arena fight. That is 65 and who knows how many times being ripped apart by rage-people and watching it happen to his friends. Holy shit... it's really a mercy that he doesn't remember.
- After a certain point, Ezekiel decides to lock Baird, Stone, and Cassandra in a room while he goes on ahead because he can't even bear the thought of watching them die again. Despite always acting like he only cares about himself, it's clear that his friends really do mean a lot to him, and being forced to watch them die over and over again due to his failures has taken a real toll on him. For a lighthearted series that clearly runs on Narm Charm, this is a legitimately dark and serious moment.
- This bit of dialogue, before the two colonels story. You can really see Baird's care and worry.
- When Flynn and Eve are stuck in the past Everyone is upset, especially Cassandra who is in tears and at first refuses to believe that they can't save them. Later when Jake admits he's keeping busy to deal with everything he also says that Ezekiel is pretending his fine and Cassandra isn't pretending she's fine.
- Flynn crosses the Despair Event Horizon in "And The Fangs Of Death" when he thinks Charlene is dead.
- Also, the explanation why he leaves at the end; he blames himself for not seeing through Apep's trap and getting several people killed and goes off to find Charlene without everyone's help because he is afraid that he might get them all killed if they come with him.
- Jenkins speech to Ezekiel in "The Apple Of Discord" It's clear the pain he felt when he was explaining how he doesn't want to choose as he is leaving the conclave. If you look on Ezekial's face at the end, he is affected by the speech.Jenkins: So why choose, 'cause nothing, God nothing, ever changes.
- In the episode "And the Wrath of Chaos" Jenkins explains that Flynn was going to sacrifice himself to stop ApepThe other librarians and Eve are horrified to learn this.
- When Flynn abandons the library before the tethering ceremony leaving Eve alone, implying that she might head down a similar path to Nicole.
- Nicole being imprisoned in the past for centuries after a mission with Flynn went wrong.
- Jenkins' death in "The Trial of the One."
- Nicole's betrayal and being behind basically everything that's gone wrong for the Librarians in Season 4 from causing Flynn to resign, Jenkins' death and Jacob, Ezekiel and Cassie resigning all so she could destroy the Librarian just because Flynn wasn't able to save her. She tricked and used everyone from the moment she met Flynn again, along with Baird and the other Librarians in the present.
- Fortunately undone in the next episode.
Tear Jerker / The Librarians (2014)