Hi, I remember seeing a theory somewhere that Pennywise and the Crimson King were one in the same. I can see some connections.

Pennywise is actually a giant spider. CK's 'son' is a spider, plus the fictional Stephen King saw a horde of red spiders in a barn.
When looking into spider-Pennywise's eyes, he partially saw its TRUE true form, some kind of reddish shape.
I haven't finished Insomnia yet, but they both inhabited Derry.
Not sure how canonical they are, but I BELIEVE that in the Dark Tower comics, CK is portrayed as a giant red spider.