The core rulebook for the Rocks on the Other Side RPG introduced you to a few beasts that you could use in your game. The Rocks on the Other Side Book of Beasts gives you nearly 70 beasts that you can use in your game.
Included in this book are the beasts from the original rules, plus many many more. You now have all kinds of mutated animals, plants, and monsters that you can challenge your players with.
Sentient molds, undead,...