Every Hidden Pennywise From IT Chapter 1 & 2

2. "Bev's" Shadow - It Chapter Two

As each of the kids experience flashbacks of their "lost day" after the rock fight - all of which they had suppressed out of their memories so much that we didn't see them in the first movie - to try and trace their artefacts, Ben heads back to school.

There, he mentally retraces his steps back to the classroom with a projector and finds himself face-to-face with Bev, alone in the classroom. She's more flirty than usual and he leans in for a kiss only to be brutally rebuffed and called fat and gross and disgusting. Then her hair explodes into flames, somewhat uncharacteristically. Turns out, it's Pennywise in disguise, which we should have known already because her shadow casts the perfect outline of Pennywise on the projector screen.

It's a more obvious one, but props to the film-makers for the double bluff.