It Chapter 2: 15 Insane Hidden Details You Definitely Missed
14. The Familiar Clown
After Bill realises that Pennywise intends to kill Dean to remind him that he couldn't save Georgie, Bill takes it upon himself to chase after the kid to save him. Naturally, this leads him to the funfair, because nothing creepy ever happens at those.
When he arrives, he chases Dean into the fun house through the mouth of a clown, because that also isn't just massively creepy and doesn't foreshadow anything catastrophic happening.
As soon as he enters, he should have known something was up, because he's immediately met with a room of swinging clowns. And just like the first movie had a doll styled on Tim Curry's 1990 Pennywise, half of the clowns in this room are dressed in his costume as another nice little callback.