Ok the true Easter Eggs after (?) joke, is about the Angel Elite Quest. You can find a lot of clues in popag's library. In that place you can realize that the riddle is about of the order of creation of races that are showed at box of southwest corner.
Edit: NO, not at library I was wrong, after a lot of tries to open the cage, an interlude appears, then if you go to Toppo Popag, he will tell you all the clues that you need. BTW sometimes I open the cage but the Easter Egg doesn't appear.
He will tell you next clues about the right order:
1. Udjos.
2. Fishterns.
3. Kazas.
4. Gazhes. (ok this race is not common, because the book of them story is bugged at ch 1, I shopped 2 times and never get it on my inventory) ok: just select race of Muraudar Clan.
And the final race looks with wings (yea, Zhyon race was the last and more powerful creation).