Karloff is a notably thin Kaiju as opposed to its more heavily muscled brethren. It has a large long head, with two sets of double eyes. Its skin is grey and leathery, with brown and red marking on its shoulders, back, fingers, and chin.
The Pacific tracking network first spots Karloff making its way to Vancouver. With the line of battle-ready Jaegers weeks away from official deployment, the Pan Pacific Defense Corps decides to deploy the Mark-1 prototype, Brawler Yukon, to defend the city.
Halfway through the city, Karloff's path is cut off by Brawler Yukon. Karloff charges the Jaeger not a moment after. However, it is quickly overpowered by the Jaeger's strength and forced out of the city by the combined efforts of the Jaeger and a volley of missile fire. Karloff is killed from a blow to the face.
- Karloff is modeled after the likeness of Boris Karloff as Frankenstein's monster in the 1931 film of the same name.
- Karloff was originally designed with a second mouth located in the center of its chest. However, del Toro believed it was too "obscene" and it was removed.
- Pacific Rim suggests Karloff is the Kaiju that attacks Manila in 2014, which would contradict its first appearance in Tales From Year Zero.