Skulkin

The Skulkin were the main enemies of the Ninja in 2011

Movie
In the Movie, most skulkin were lightning skeletons, with blue armour and sometimes a black army hat. Also, Krunch was given a red belt (instead of grey), and a black helmet (instead of, once again, grey).

Kruncha and Nuckal
In the movie and ultimate guide, Kruncha and Nuckal have different personalities.

Kruncha
Movie: second in in command, strong warrior.

Book: dimwitted, yet extrememly strong and brute, warrior.

Nuckal
Movie: child-like, unintelectual warrior.

Book: Second in command, smart.