Hippo Hero Achievement in Halo: The Master Chief Collection

Although this hidden Easter Egg is difficult to explain through text, go ahead and start up a Forge Session on Foundry. As soon as the session begins, enter Editor Mode and travel to the middle of the map. Staring towards the back wall of the warehouse, pan the camera down slowly. You should see a couple piles of trash on the floor, though you’ll want to approach the small trash pile on the right. If you get close enough to the floor in Editor Mode while scanning this trash pile, you will see a stuffed hippo lying in the waste, staring right at you. After looking at the hippo for a few seconds, the achievement will unlock.