The main driving force behind this book is the sheer ease of creating monsters for ZWEIHÄNDER. In the MAIN GAUCHE Supplement there are really simple to follow rules that allow you to create your own beasts and abominations.
The bestiary in the core ZWEIHÄNDER rules is supposed to be comprehensive but I defy any Game Master to resist throwing something completely new at their players. ZWEIHÄNDER is a fairly young game and I doubt if there are many players who have memorised all the stats for all the monsters but it will happen. When it does having monsters that no one knows puts the surprise and wonder bank into a game.
Folklore plays a big part in ZWEIHÄNDER. If a character knows all about a creature then it falls upon their Folklore skill to say whether they know about it or not. When a GM introduces a new monster they get a chance to add an entirely new folklore into their world.