Not even the prologue can escape this. It starts off with peaceful sequences of woodland creatures in their habitat. At the end of the prologue, the same sequences repeat, this time with their forest destroyed, setting the tone for the rest of the film.
Robyn accidentally shooting Merlyn with her crossbow, devastated that she's possibly killed her beloved pet. It gets even more dire when Mebh appears and takes the wounded Merlyn into the forest with her, and Robyn tearfully begs her father to let her search for Merlyn, clearly worried about what might happen to him.
Although it's initially Played for Laughs, Robyn is setting herself up for a big disappointment when she pretends to have a conversation with her dad, right down to imagining he'll promise he won't get angry. When he comes home and Robyn asks him to promise not to get angry, you know it won't go well when he doesn't actually promise. When she mentions going back into the woods to find Merlyn, Bill does indeed get worried and upset, scolding her for disobeying the Lord Protector's orders to stay in the town. And Robyn, on the verge of tears, doesn't even get a word in edgewise and share her diplomatic idea of letting the Wolfwalkers leave peacefully.
During her first day of work as a scullery maid, Robyn is clearly unhappy while doing the numerous chores around the scullery, particularly when the soldiers march through the hall she's helping to clean and track muddy footprints behind them, which add even more to her workload. Then she turns to the elderly scullery maid, worried that one day she'll end up just like her: old and having wasted away her life.
After running through the woods as wolves, Mebh and Robyn soberly note how the woods are growing smaller every day; the great oak they stand at was deep in the woods the previous day, and now it is at the edge of the forest.
The very next evening, this big proud oak tree has been felled.
Moll: Only a Wolfwalker can make another. When did it happen to you? Where? Is the wolf that bit you near? Is she alright? Is she alive? Where is Mebh?
While the audience is supposed to hate the Lord Protector for being an unpleasant and horrible man who wants to crush everything the Wolfwalkers stand for with an iron fist, him praying to God is oddly poignant. From where he stands, he's trying to run a small town without letting it fall to rioting, which isn't an easy feat. As he puts it, he was hoping to come back to less problems in Kilkenny, only for his worst fears to be realized. That doesn't mean we're obliged to like him, but it does make him more human.
There's something disheartening about seeing Bill demoted by the Lord Protector, from his rightful profession as a hunter to a mere foot soldier. Being a hunter is what Bill excels at, and not only does the Lord Protector take that away from him: he demeans him at being a failure at one.
Later, when Bill starts his first day at his new profession, there's the visual of Bill and Robyn being pulled apart to their respective new jobs (foot soldier and scullery maid). It's a sobering symbol of how the Goodfellowes' efforts to stay in line is steadily tearing them apart as a family, and how they're being forced to work in jobs that neither of them want in order to survive in such a strict, rigid society.
Mebh talking about Robyn with her mother's unconscious human body; at first she happily talks about the new friend she made, but soon she's tearing up and asking her mother where she is as if she could respond. Beneath Mebh's boisterous exterior, she deeply misses her mother's actual presence and fears being alone. All she can do is tearfully snuggle up to her mother before she turns in for the night and tries singing herself to sleep.
After urging Merlyn to pass on her message to Mebh, Robyn essentially sets him free into the wild. She feels she has no choice but to give up on her dreams and resign herself to spending the rest of her life as a scullery maid, even though Merlyn's expression clearly shows that he doesn't want to leave her.
Robyn: Merlyn, I can't get out to Mebh. Find her. Tell her to leave. Lead her away. She must go. [tearing up] At least you can be free.
Robyn's second day working as a scullery maid. As opposed to her previous night running through the woods free and happy, Robyn is absolutely miserable. The work is even more tedious, mundane and soul-crushing than it ever was the day before. She'd try to sneak out if she could, but between Moll's plea to protect Mebh and her fear of getting killed as a wolf, she feels she has no choice.
Robyn telling Mebh to take the pack and leave the forest, despite Mebh's tearful imploring that Robyn promised to help her. She's doing it because she made a promise to Moll to make sure her daughter was safe, but it's still a sad and painful scene since Mebh doesn't understand why Robyn isn't helping her find her mother like she promised. Gripped with anger and grief at essentially being betrayed, Mebh takes the flower Robyn gave her which represents their friendship and crushes it in her hand before angrily throwing it on the floor and running off.
Later, it becomes a real betrayal when Robyn has the local children put Mebh in a cage in order to keep her safe. The sad thing is, it parallels how Bill has been putting Robyn in a metaphorical cage, because she's been taught that's how you protect those you care about. To twist the knife in further, she uses the same words her father used to justify locking her in town.
Robyn: Mebh, your mother told me to keep you safe.
Worse still, it's more heartbreaking when one thinks back to all the times Mebh stubbornly insisted "Nobody can catch my Mammy." All of a sudden, all her worst fears are being realized: her brave, free-spirited mother has been captured and chained up.
Mebh angrily declaring to the townsfolk that she will lead the pack to free her mother, then destroy the town and eat all of them as revenge for imprisoning Moll. While it counts as an Awesome Moment, it's also a sad one, since Mebh is so overcome by anger and grief over seeing Moll in chains that she's willing to resort to extreme measures to rescue her mother. Thankfully, Robyn frees Moll before this can happen, but Mebh still came dangerously close to becoming the monster that everyone thought the wolves were.
What's also sad is that this is the result of Bill succumbing to his fears, and it causes him to nearly kill an innocent person.
Robyn having to reveal that she's a Wolfwalker to Bill after he mortally wounds Moll and causes her wolf form to dematerialize. Bill's realization that she was telling the truth the whole time leaves him with so much to take in: he had previously tried to kill her without knowing it, and even nearly destroys his relationship with her over someone actually human. It's even worse when Bill hugs her, thinking that Robyn will stay with him, but then, Robyn transforms into a wolf and decides to leave Bill. And now, she's seemingly done so forever to help her friend (and without saying goodbye), even after Bill's constant pleads to stay with him. In the end, he has nothing left except his daughter's unconscious human form. The whole thing leaves him completely distraught.
Robyn:[trying to follow Moll) Mebh! No! I have to help her! She's dying!
Bill: Come on, Robyn!
Robyn: Let me go! Mebh! Mebh!
Bill: No, Robyn, why?! I don't understand!
Robyn: Don't you see?! I'm one of them! I'm a Wolfwalker!
Bill:[gasps] No, Robyn, please! Stay with me! I can't let you go!
Bill:[Hugs Robyn, thinking that she decided to stay]
[Unfortunately, Robyn's soul leaves her body, taking the form of a wolf]
[After she materializes, Wolf Robyn looks at Bill sadly]
[Wolf Robyn winces after looking at Bill sadly, and runs away to Mebh. Bill is left crying over Robyn's body as the Lord Protector and his army appears right behind him.]
If you thought Bill's reaction was bad, think about what Robyn went through after seeing Bill shoot Moll: it's established that through her eyes as a Wolfwalker, she can see other Wolfwalkers in their wolf form as humans, and presumably vise-versa. So Robyn during the dematerialization scene is basically seeing Moll's dying spirit as a human, slowly floating away. It's traumatic for her even more so than Bill.
In the third act of the film, Bill resorts to shouting at Robyn, taking out all his frustration with his life on her in the process, when she begs him to free Moll as a wolf. When Robyn decides to stand up to Bill and free Moll herself, all Bill can do is beg her to follow the Lord Protector's orders. He confesses his fears of her being captured, but sadly, Robyn just angrily snaps back at him for not understanding her stressful situation. Sure, it's sad to see him become so desperate, but he's also afraid of losing probably the only family, the only light he has left in his life.
Bill: I won't be here to protect you forever. [hugs Robyn] I'm so afraid that one day, you will end up in a cage.
Robyn:[pushes Bill away] But I already am in a cage!
When Bill shoots the wolf Robyn was with (which was actually Moll), thinking that he's saving her, it turns out that the wolf wasn't there to hurt her. Under the thought of protecting her, all Bill did was strain the relationship between him and Robyn, and because of him, his greatest fear nearly came true.
Bill ends up lamenting over the damage he has caused during the forest fire, while carrying Robyn's unconscious human body and begging her to wake up.
The second half of the climax where Mebh tries to use her powers to heal Moll's arrow wound. She keeps trying, but it's apparently not going to be enough to save her mother, even when she gathers the other wolves to lend their power. When Robyn comes to help Mebh by combining their wolfwalker powers in a display of sisterly love that saves Moll, those sad tears turn into Tears of Joy.
After helping revive Moll, Bill turns around and prepares to leave the cave upon seeing her, Mebh and Robyn happily embrace, regretful of the harm he inflicted upon them. Even as a Wolfwalker, he feels that he has completely alienated his daughter and has no place in Robyn's new life. However, Robyn and Moll are able to convince him to stay.