From the publisher:
This appendix is filled with new creatures for the Spelljammer universe, and it highlights the creatures of Wildspace; new and savage outer space creatures.
From the back cover:
Prepare to be boarded! Here are still more new, inventive, dangerous, and entertaining creatures and races for your Spelljammer campaign setting! There are giant undead insects, star gypsies, space plants, and much, much more awaiting your stellar travelers in these pages. Elven war-beasts, giant space turtles, orcish death-creatures, and other beings of the phlogiston, crystal spheres, and wildspace roam this volume. Some look nasty, and are; some look nasty, and aren't. Which are which? Read the entries and find out for yourself! And of course, they are organized into five-hole-punched pages that fit right into your Monstrous Compendium binders.