Sansom revealed that the smile and eyebrows are the key to making this clown look truly depraved. "[The lines of] his lips go up through his eyes and eyebrows," he explained. "His eyebrows are very angular, and they can be very sinister-looking without him actually having to make any facial expression."
If your eyebrows aren't quite as evil-looking as Pennywise's, don't worry. You can cover them up using a gluestick or concealer, and then draw on your thin, angled brows with makeup.