The 5th ed. D&D Monster Manual only has 8 fey creatures included. Monsters of Feyland has 100 fey creatures listed, along with multiple Feyland Features and Flora. MoF has plenty of unique fey creatures, such as the Jabberwock and Quadrak dragons, the Lake Gnome, the Rainman, and the Huntaur. Also included are exotic variations on some classic fantasy creatures, such as Black, Green, and Red Unicorns, Lycanthropes (werebadger, werefox, and wererabbit), and Giant beasts (butterfly, dragonfly, fox, rabbit, swan, and tortoise). If you're looking to run any type of fey realm fantasy adventure, this is the book you need.