Although, Dr. Cheon/Talisman is rather slow to get started IMO, but when it hits its stride about halfway through, the mixture of supernatural events and headlong action is head-spinning.
Excellent performances from everyone, with a particularly terrifying performance from Huh Joon-ho as the "head demon."
Although I was not fully clued in to the Korean mythology at all times, if you just go with the supernatural flow you'll find the film a delightful mix of fantasy, swordplay, and some classic car-crashing, fist-punching action.
Special credit to director Kim Seong-sik (who one of my sources indicates was an AD on "Parasite") and editor Gang-hee Lee (and the entire production team) who really crank up the energy via practical action, crack cross-cutting, and stunning VFX.
I only hope this talented cast and crew can come back with a sequel. I'm ready for a whole series of Dr. Cheon flix.