To get Eastereggs you have to carry out fixed actions in the right order. Depending on the Easteregg it needs a different number of actions. There are some, which need only 2 steps to do (like Seraphim in Edain 3.8.1), but also a few, nobody knows anything about how to "find" them (like the Overlord). Also, Youtuber RuudDevil is doing the Easteregg videos where he clearly explains how to get one or other easteregg so watch them on your own risk (SPOILERS!). But before watching the videos try to solve these riddles.