Won't Ask Where it Kept That
From RoR Wiki
Instructions: Order & Destruction
Kill the "Unmounted Manticore" in Saphery at 53.9k 19.6k, above the waterfall. It will drop a Pocket Item "Partially Digested Manual", equip it for the unlock.
Note: You can also find other "Unmounted Manticores" near, around 54.5k 15.7k.
- XP: 336