Monster Mash: Monster Classes for Basic-Era Games

From publisher blurb:

Here, there be Monsters!

For years brave adventures have been going into dark dungeons and fighting monsters.
Now the monsters are fighting back.

Monster Mash is an Old-School Essentials Classic Fantasy compatible game supplement that allows you to take on the role not of a stalwart hero but as one of the monsters.

This book features 13 horror-based classes.
The Awakened Golem, Cat Folk, Ghosts, Haglings, Hobgoblins, Revenants, Shadow Elves, Shades, Werewolves, Wererats, Vampires, Profane Necromancers, and the Gothic Witch.

New spells for Haglings, Profane Necromancers, Shadow Elves, and Gothic Witches.
New occult powers ritual spells for Gothic Witches.