KeyForge: Menagerie decks provide their own unique KeyForge experience, each fully playable deck includes at least one of many different Menagerie packets.

Each Menagerie packet is a group of specific cards chosen from the entire KeyForge card pool. 

Each packet has a name and theme, designed to give a deck a special feel or identity that in the past was either very unlikely, or potentially impossible. 

There are many different types of Menagerie packets such as the gigantic cards, creature groups, special combo card constellations, and special themes.

KeyForge: Menagerie decks are intended as fun and casual play experiences, ideally with two Menagerie decks facing each other. 
While each KeyForge: Menagerie is a unique fully playable KeyForge deck, they are not legal in official KeyForge tournament play.