Within the game, try typing the following words at appropriate places. Before trying any of these, be sure to save your game!
mikespants = type this at any point in the game, then navigate through the Easter egg screen.
eat me = type in front of the skeleton in the Hades Subway Station
whoami = type this at the credits screen and you will get a list of people's names who worked on ZGI. Clicking on a name will type out a personalized greeting from that person.
killmenow = type this at any point in the game.
huisok = Type this at the phone in Hades just before solving the damn phone puzzle.