OK...Let's start with the monsters:
Vile Addiction introduces the Child of Sehan: 'Covered with a layer of viscous slime, this humanoid-shaped mass of roots and vines lumbers along with the gait of a drunken man. The fibrous green tendrils that have been woven together to create its form constantly writhe and pulsate in an oddly familiar rhythm. A sickening stench and a faint sloshing sound mark its steady advance, and its eyes glow red' - A CR 8 vegetal montrosity with a hypnotic gaze & a deadly, poisonous touch that transforms those who succumb to it into a fellow Child of Sehan.
City of Broken Idols includes a number of unique, templated foes, but only one new monster: The Skinwalker: 'This humanoid figure is armed with a sword fitted with jagged ridges of obsidian and a shield that bears an image of a two-headed tentacled beast, yet he is no man. He wears what appears to be the hide of a demonic lion. The underside of this skin is raw muscle, fusing to the man's skin and becoming one with him. The beast's head rears up around the man's head, while its arms, hanging down from the man's shoulders, writhe like snakes ready to strike' - A CR 6 outsider, the result of a fusion between human & jarilith demon, the culmination of a foul rite of Demogorgon. Skinwalkers seem to rely on physical attacks and poison-coated weapons to bring down their foes, & are strengthened by a few immunities, the result of their demonic heritage, presumably.