Johan Egerkrans Vaesen is excellent and a wonderful source of inspiration for Væsen.
Another wonderful book is “ Julebestiariet”, it 24 Creatures from European folklore, that are somehow connected to Christmas. The illustrations by John Kenn Mortensen are really cool, I’m a huge fan of his work.
However, I think the book is only in danish, which should be ok for anyone who speak Norwegian or Swedish.
Link : https://cobolt.dk/shop/julebestiariet-501p.html