The role monsters play in Colonial Gothic will depend on the sort of game you like to run. If you play the default 'Gothic Horror' style of game, monsters are best used sparingly but to good effect as you build up the evidence and the tension until whatever creature is behind events is revealed. A 'historic fantasy' game might have a fair few monster encounters, just as any other fantasy game does. And if you enjoy the political aspects of the game, most monsters come on two legs! My own games, which are alternate-history with an interest in exploration and discovery, however, can find a use for a monster or two...
There are over 50 monsters here, some are 'real' beasties - this doesn't detract from the threat they pose, take the alligator for example! - and others more fantastical, the beasts of myth and legend. Notes are provided as to the source of each one, useful if - for example - someone versed in the appropriate traditions is able to identify a given monster by matching the evidence to the legends that they know.
Each monster comes with an illustration (many very appropriate to the period in style), a stat block and notes giving all the game mechanical information that you need to run them, and further descriptive notes coverning appearance and giving ideas about how they might be used in your game. Many are quite scary and characters encountering them will have to make a Fear test to do anything but run screaming in terror!
The PDF version is comprehensively indexed, and there is a useful appendix which lists creature types and presents a combined listing of all monsters in this book and the core rulebook. In fact there are 2 lists, one being alphabetic and one by creature type to aid you in finding the right monster for your needs.
A good addition to this game line which should find plenty of use!