Issue 20 opens with Zim creating the Conquer-Blob, a creature whose one purpose, driven into its every cell, is to crush humanity and conquer the Earth for Zim. A week later, the Conquer-Blob emerges from its containment in Zim's lab, ready to fulfill its purpose. However, by this point, Zim had grown obsessed with Floopsy Bloops Shmoopsy, a show that GIR introduced him to. More focused on watching it than his previous plans, Zim tells the Conquer-Blob to go about its business, saying that he'll catch up when he's done.
Within a few months, the Conquer-Blob has successfully destroyed all of human civilization, reducing it to flaming ruin, and telling the humans gathered around it that it has done this in Zim's name. However, Zim is still watching the show, and never shows up. A year later, the Conquer-Blob is still in front of the crowd and is playing games to pass the time. In the meantime, it appears to have gotten to know the humans surrounding it personally.
Some time later, after much consideration, the Conquer-Blob has changed its mind about conquest. It restores human civilization and, after saying goodbye to a now grateful crowd of humans, flies off into space to find other people to help.