I want to give a more detailed explanation for Immobile.
An immobile ninja cannot perform any action for 1 turn, be it a mystery skill, standard attack or chase. If the ninja is channeling a mystery skill it will be interrupted. If the ninja is status immune and he is channeling a mystery skill it will not be interrupted (just like in SA).
Furthermore, if the ninja has already performed his action for the round and he is immobilized, unless cleansed the immobile status will remain for the next round.