The 2017 adaptation of Stephen King's It helped ensure that a healthy fear of clowns made its way to the next generation, but Pennywise isn't the only form It takes in the film. It is a horrifying entity that chooses to appear as the dancing clown most of the time, but It can be many things. It chooses its form according to the maximum psychological terror it can inflict.
In Stephen King's book, It tends to stick to classic horror movie monsters like mummies, werewolves, and Frankenstein's monster. Sometimes, though, It transforms into something deeply personal. Whatever It appears as to you is chosen because It knows your deepest fears.
In the 1990s, It was played by Tim Curry, who set the standard for modern spooky clowns. In 2017, Bill Skarsgård took on the role, and he reprised his version of the ravenous monster in 2019's It Chapter Two.
In the 2017 film, It appears to the Losers Club in many different forms, each one more haunting to the poor kids of Derry. These are all the different monsters and forms that It takes in the 2017 film.