Gleanings from the company website, this contains a wealth of snippets to add in to adventures set in the Old Margreve forest and round about. To start with there are 20 beautifully-described NPCs, provided to help you bring the place to life. They aren't intended for combat-fodder, if you do want to involve them in a brawl you'll have to provide your own stat-block... but as part of life's rich tapestry, people living and working in the area who might interact with the party, they're excellent. Watch out for Shadow, a black dog belonging to Tsarin the Dirgist. This hound has an uncanny nose for when someone is about to die, and leads his master to the spot so that he can perform a funeral dirge and eulogy for the just-departed. Some say that Shadow's appearance heralds (or even causes) the death... or is it just that he has impeccable timing?
Next up, 25 'reskinned' creatures, that is, the specifically Margreve versions of monsters from the Pathfinder Bestiary and Bonus Bestiary. These just come with descriptions again, but there's an indication as to which monster from the Bestiary you should reference. It's a neat way to put a twist on the creatures you encounter without much effort, and helps make the locale more distinctive.
Along the same theme, there are 15 reskinned spells, which can be used in different ways as you please. It may be that locals use these distinctive variants of spells that the party is used to, or - and this could cause some surprises - it may be that the spells act this way when cast in the Margreve, be it a native or visiting magic-user that casts them! If you decide they are local variants, others may learn them in the usual way... but may find that once they've left the Margreve they don't work as they need local components. Following on from that, there's a Margreve Bloodline that lets sorcerers tap into the ancient powers of the old forest and even become a part of it. If the Margreve is part of your campaign world, a sorcerer may have it - he doesn't even need to be local as long as he's descended from someone who was.
There's also an incantation, a few fascinating local items, and a selection of traits available to anyone who grew up in the area. It's all added flavour, and well worth picking up if you're using the Margreve. The illustrations are rather good - and evocative - too.