- "Turn the darkness... into...◊ (creepy distorted voice) light."
- This needs elaboration: Aisling helps Brendan find Crom Cruach's cave, but partway in, the ceiling starts collapsing, prompting Aisling to hold it up while Brendan makes his way further in. After getting to relative safety, Brendan turns back to see her, now weakened and emaciated, and we get that lovely view of her face for just a second before the cave collapses on her.
- Crom Cruach himself (his design is inspired slightly by the writhing dragon forms in Celtic artwork and mostly by everything scary that lives in the deepest seas) and his ultimate fate involves eating himself.
- The attack on Kells. So much. Seeing Abbot Cellach struck down, after it'd been shown that he was the strongest out of all the people there. Not to mention the collapse of the scaffolding...
- You only see the top of Crom's cave from the outside in a shot or two—it seems to have a spiky design on it. According to the DVD Commentary... it's the blood of Crom Cruach's human sacrifices.
- The Vikings in general. Huge, hulking figures with glowing red eyes that speak a guttural, growling language.
- This movie does not gloss over the destructiveness of the Viking raiders, and while most actual deaths happen offscreen, it makes it painfully clear that an incredible number of people were killed. Crom Cruach is also quite likely to scare the pants off unsuspecting viewers.
- Brendan and Aidan having to leave the Abbot behind to die because there's nothing they can do to save him.
- Brendan's Prophetic Dreams. As simplistic as the design is, it's rather horrifying seeing the vikings slaughter people and Dream!Brendan being subdued by Dream!Cruach.
Nightmare Fuel / The Secret of Kells