The borough boss drop, one rung below the Map of the Stars in the mimic's reward hierarchy.
Carl knew the boss-drop hierarchy from The Dungeon Anarchist's Cookbook and Mordecai: neighborhood bosses drop The Neighborhood Map, borough bosses drop the field guide, and the Station Mimic — larger than either class — dropped the Map of the Stars instead. He looted it from the gore knowing it had arrived too late in the floor to be much use.
A boss-drop guidebook, referenced only by tier.
Mid-tier boss drop used to place the mimic's reward in context.