This game contains only one easter egg as far as we know, which is the Oryx Statue. For this easter egg you need a trickster with a prism that can teleport you to a target or a rogue with a Cloak of the Planewalker.
What you need to do is go to your vault and teleport out of the main vault area. Now you stand on grass. Walk around the tiny island and another island will pop up on the map. Once you see it, teleport twice to get to it and then you see another island. Keep teleporting untill you reach the easter egg (this is also a way to get out of the nexus).
If you use a Magic Mushroom while near the Statue, you will see (hallucinate ) that the Statue transformed into one big random thing in the midle surrounded by 8 other small random things. Some say that if you use a Wine Cellar Incantation on it, it will awake and you will have to battle Oryx alone. Although this is not confirmed, Private Servers can make this possible.