Age of Empires II: Definitive Edition (PC) - Achievement - Eternal Gratitude
Encounter a Penguin in the Historical Battle "Vinlandsaga".
This achievement is one of the simpler mission achievements. Start by building a Transport Ship and load one or more unit on to it, then just send it to the top of the map where Greenland is (that's where the Penguin resides). Land on the Northern-most section you can and simply follow the land sticking as close to the top as you can. You'll find it just behind some rocks before you get to the Greenland Market and University. The Penguin actually joins you as an attacking unit too.
*EDIT* - 05/01/2021 - Multiple reports have been made of a recent update affecting this achievement that may stop people from getting it which if true, will hopefully be resolved soon.