You will receive a quest early on in the Grasslands, to repair a farm from Bushel. Once you've cleared the Murk and placed a large animal pen, you will be tasked with befriending a Groffle. You will need a stone and Celium flower to craft Celium seed to tame it so it will follow you back. Once you reach the animal pen, you will have an option to adopt the Groffle. Select yes to unlock the achievement.