The ending of 'IT: Welcome to Derry' has been explained, with outlets discussing how Pennywise is defeated and the implications of the finale. The season 1 ending involves a time travel twist and a surprising connection to the films, with some characters living and others dying. The finale's epilogue has also been explained, including a cameo that was reportedly a last-minute idea, although the specifics of the ending and its consequences are still being clarified.