It's a horror series. Natch. From the first book alone we have...
A boy with tiny worms swimming around in his blood.
The same happening to the father, as the boy watched. He also watched his mother and father burn to death.
Anthropophagi. See here for a lovely picture by Keith Thompson.
Crawling around in the dark and mud in tunnels dug by man-eaters as they hunt you.
The second book has Will Henry bitten three times, once by a regular monster but twice by the human-turned-Wendigo Chanler. It falls into squick pretty quickly because Chanler only wants to eat Will's heart and tends to caress him while trying to kill him.
The first book also features a man being [eaten alive by a maggot infestation. When his boots are pulled off, most of his skin comes off with it in a detailed description including a waterfall of bodily fluids.
In the second book, the Wendigo wears the face of his victims over his own. Chanler wearing the face of Muriel kisses Pellinore in a sewer where he also happened to kill a baby.
Will Henry sees the baby's mutilated body and face floating in the sewage.