I watched NGTZombies easteregg steps, first steps they did was retrieve 5 crystal skulls with the tomahawk.
They then threw the tomahawk through the poster in one of the cells. After that you have to find 3 spoons I believe and retrieve them with the tomahawk. When you retrieve the spoons the voice will tell you the prisoners numbers that you have to put into the number machine that let down the rope for the plane. After that there will be headphones that look like drops leading up to the roof. After you receive all the headphones and listen to the history, all players need to go to the back of the plane and take it to the bridge. On the bridge your bodies will be at the electric chairs, revive your players, and kill the weasel. It then ends your game. Pop goes the weasel