From Melvor Idle
This page is up to date (v1.2.2).
Pet ID: melvorAoD:MapMasteryPet
Source: Cartography
Drop Chance: See: Acquiring Pets
Effect: Doubles the effects of all positive Active Modifiers from Point of Interests in Cartography
Part of 100% Completion: Yes

Carthulu is unlocked after 944 Hexes have been Mastered in Cartography. When a Hex is surveyed up to Level 5, it will become "Mastered". The option to do this for Level 2 Hexes is unlocked after you survey the entire map for the first time.