When David keeps having nightmares, and blames Hilda and her scary adventures for them, Hilda and Frida try to help David to face his fears. However, in the process, the trio soon finds out that his nightmares are not natural, but are caused by a malicious nightmare spirit known as the Marra, who feeds on the nightmares of others.
Tropes:
- Absurdly Spacious Sewer: The sewers of Trolberg are a big, underground complex of tunnels.
- Bedsheet Ladder: Hilda and Frida use one to secretly let Frida into David's room.
- Break the Cutie: Hilda takes it hard when she suffers her nightmare. It's hard to see this sweet blue-haired girl scream.
- Catapult Nightmare: David is seen waking up like this after the Dream Intro.
- Clothing Switch: David and Hilda switch clothes (and wear wigs) to disguise themselves as each other so Hilda can spend a night in David’s room and confront the Marra.
- Dream Intro: The first scene of Hilda, Frida and David exploring a dark storm drain tunnel is eventually revealed to be a nightmare of David.
- Dream Within a Dream: After the Marra takes Hilda’s challenge to give her nightmares instead of David, we see Hilda seemingly having one, then waking up. Except she didn't wake up; that was part of the nightmare.
- Face Palm: Done by Frida when Hilda offers to help David get rid of his nightmares…by finding the rat king.
- Foreshadowing: While Hilda and Frida are chasing the Marra, a poster of The Black Hound can be seen on a wall behind Frida.
- Halfway Plot Switch: The episode starts with Hilda, Frida and David going into the sewers to seek out the Rat King. After he reveals to them who the true cause of David’s nightmares is, the plot switches to Hilda and Frida tracking down the Marra.
- Giant Wall of Watery Doom: Downplayed, but Hilda, Frida and David are surprised by a huge wave after entering a storm drain. It flushes them deep into the sewers.
- Knowledge Broker: The Rat King loves to hear secrets, and will trade them for others. In return for a secret told by Hilda, he reveals the teenage girl they saw earlier is the one causing David’s nightmares.
- Interrupted by the End: Following their ordeal, Hilda apologizes to Frida and David for dragging them into something scary. But they respond by telling her that doing this is what they like about her. Frida then asks Hilda what they should do now, and her response is asking Frida and David to teach her ride a bike. Cue happy credits music. Viewers never got to see Frida and David helping Hilda out with her bike problem.
- Nice Job Breaking It, Hero: The secret Hilda told the rat king in return for him telling her about the Marra is eventually used against her by the Marra; the secret that she can’t ride a bike.
- Not Helping Your Case: Hilda tries to justify her actions for seeking out a rat king by telling David it won’t be so scary anymore once he actually sees one, like trolls. Then she goes into details how trolls eat humans, prompting David to snark that will most likely be his next nightmare.
- Out-of-Character Alert: David inadvertently blows his cover when Hilda's mom comes into the bedroom clearly puzzled that "her daughter" would be snoring so loudly.
- Rat King: The protagonists encounter one in the sewers of Trolberg.
- Scary Flashlight Face: At the start of the episode, Hilda does this as she, Frida and David are about to enter a tunnel.
- Sentient Vehicle: A demonic car appears in Hilda’s nightmare.
- Take Me Instead: To make the Marra stop bothering David, Hilda calls her out for picking on an easy target, and challenges her to try and scare someone who isn't so easily frightened; herself. The Marra agrees. When David sees Hilda struggling with a nightmare, he offers to take the Marra back. This prompts her to leave both David and Hilda alone since it's no fun to torment a willing victim.
- The Reveal: Hilda's nightmare reveals she has an inability to ride a bike. The episode ends with Hilda asking Frida and David to teach her how to ride a bike.
- "What Do They Fear?" Episode: Since the Marra use a persons' fears to create the nightmares, this episode turns into one. For David, he's afraid of pretty much everything, but the Marra specifically focuses on his fears for the Rat King and Trolls. Hilda proves a more difficult target, but eventually the Marra finds something she fears; her inabiliy to ride a bike.
