In Lost Ark, Mari's Mechanical Doll is a collectible entry in your Adventurer's Tome. It can be found only in the Arthentine Continent, appearing randomly every so often.
Where is Mari's Mechanical Doll in Arthentine?
Larger monsters tend to drop Mari's Mechanical Doll more often. You can increase your chances of finding Mari's Mechanical Doll by going straight for the special monsters.
The method of earning collection items isn't set in stone. Since monsters drop them randomly, it essentially comes down to luck and old-fashioned farming. Mari's Mechanical Doll looks like a ballerina on a turning base. It's got a blue dress and looks like a doll based on a teenager.
Take it to a secluded, safe location if you intend to place it in an Adventurer's Tome. Origins of Stern is usually your best option because it's a big city and there is no danger there.
Open your Inventory by pressing the I key and right-click on Mari's Mechanical Doll. There will be a notification that Mari's Mechanical Doll Collection has been added to the Adventurer's Tome.