1. what pennywise the clown actually is. it is an orange light that mesmorizes those that are afraid. when mesmerized, IT can feed. IT wakes up every thirty years and IT feeds. It is what is behind the clown. Like Stan Uris said "I saw what was behind the clown."
I looked right into IT's... some kind of lights. I looked right into IT's deadlights.
While It can take assume any shape to terrify Its prey (ex: Pennywise), Its true form is not on earth. The true form of It exists beyond the physical, in a void surrounding our universe, known as the macroverse. It's true form is described as living, insane, writhing orange light. Direct contact with the deadlights results in instant death (with the exception of Audra Phillips who entered a deep coma). The deadlights can be seen through It's eyes when It takes the form of a giant female spider which is the most accurate shape the deadlights can translate to on earth.
Bill Denbrough is almost taken into the deadlights when he engages It in the Ritual of Chüd, under the Derry sewers in 1958 and 1985.