Pennywise takes many forms over the course of the story and the entity’s final form is that of a spider. Now, this isn’t exactly what It looks like. In the text, King makes it clear that this is the closest thing to It’s true face that the human mind can take without breaking. In the miniseries we get a janky practical effect of a large alien spider, and in the Muschietti film it’s a CGI giant Pennywise with spider legs.
In this case, the miniseries hews closer to the book, but both leave out a fascinating element: It is a she, and she is about to have a bunch of babies.
Defeating the giant spider isn’t the end of the fight in the book. The surviving members of The Losers Club also have to squash all the spider eggs, each one containing a possible new It that will continue to feed on the residents of Derry and beyond.
Considering that this could have led to a sequel, it’s surprising that Warner Bros didn’t insist on including this detail in “It: Chapter Two.” Say the Losers stomped on the eggs and think they got them all, but the audience sees one final egg left behind. It hatches during the post-credits scene and blammo, the door is open for a sequel.
That is a lot to try to fit into the finale of a billion dollar franchise, but it remains a one of many fascinating moments from the book that never made the cut in any adaptation.