https://screenrant.com/why-pennywise-lives-in-sewers-it
Because, It likes to live in a shit-pipe! Thus, it's a shit-monster from outer space.
https://en.wikipedia.org/wiki/It_(character)
The shit-spider monster can clearly alter its appearance.
"IT's true form as perceived by the human eye is that of a giant spider that houses IT's essence: namely writhing orange lights (termed "Deadlights"), looking directly into which can either kill a person or drive them insane." https://en.wikipedia.org/wiki/It_(novel)#Pennywise/It
No clown disguise, just a monstrous appearance.
https://en.wikipedia.org/wiki/It_Came_from_Outer_Space
The It monster or creature in various depictions.
https://en.wikipedia.org/wiki/It!_The_Terror_from_Beyond_Space
The THING is the quintessential monster.
https://paranormal-intersection.blogspot.com/search?q=monsters
