The history of the third island was vague.
For a very long time, countless trillions of years ago, the entire Land of Nothingness was enveloped in chaos. Gods came and Gods died. Gods populated the earth and acted as the soil that birthed later civilizations.
When the era of chaos ended, all of the islands drifted apart and a more linear trial was created for those who entered this realm. With that development, the pointless slaughter became meaningless and most people stopped their reckless actions.
From that point on, every island changed on its own, becoming more suitable for the trials in place. The first island was for the weakest of the weak, so it remained in a more primordial state. The second island was able to form something of a civilization, but many factors held it back from truly thriving.
