Invader Dib was alleged to be the three-part series finale/TV movie continuing from the end of the untitled season two finale, wrapping the series up. However, since the show was abruptly cancelled during the beginning of the second season, it was never finished or aired.
According to vague plot details and rumors that have been released online over the years, it appears that this special would have followed Tenn's kidnapping by the Meekrob, and an all-out war happening between the Meekrob and the Irkens, which would have ended with Zim (aided by Gaz) being victorious over Dib, The Resisty, and the Meekrob, and finally conquering Earth. According to at least one rumored version of this idea, Zim and Gaz would have then taken over the Irken Empire while Dib and their other defeated foes would have been banished to Saturn.
It is unknown what season this would have aired after, if at all.