The Mortal Instruments: City of Bones (2013)

Revealing mistake: Early on, after Clary blasts the demon with a homemade explosion that blows a huge fireball across the kitchen and blasts out the window, there is no sign of anything being burned, not even the curtains. The kitchen is only in a slight shambles and there are small fires burning in isolated areas that never spread or char anything.

raywest

Revealing mistake: When Jace and Clary are on the spiral staircase in the conservatory, the automatic overhead sprinklers go off. Even though the (CGI) water spray can be seen falling all around them and they are not under any cover, they are obviously not getting wet, their hair and clothes staying perfectly dry. When the scene cuts to a different viewpoint, there are some water spots on Jace's back, but they are in an odd pattern and only in a small area, not all over his light-colored shirt, which is dry. As they are walking back to Clary's room, both are still completely dry and the wet spot on Jace's back has disappeared.

raywest

Plot hole: When Clary uses the rune that temporarily freezes the demons, the group just slowly creeps past them to escape rather than destroying the demons when they're are completely helpless. When the rune wears off, they begin fighting and killing the demons again.

raywest

Hodge Starkweather: Everything you've heard... About monsters, about nightmares, legends whispered around campfires. All the stories are true.

Clary Fray: Why can I see you and no one else can?
Jace Wayland: You're not a mundane.
Clary Fray: What's a mundane?
Jace Wayland: Someone from the human world.
Clary Fray: If I'm not human, what am I?

Alec Lightwood: What is it about her?
Jace Wayland: She's different.
Alec Lightwood: She's gonna get us all killed.