Notorious Games unveiled Xsyon's unique new creature migration system. Unlike worlds where mobs are static, this sandbox will ensure that animals don't just hang around one place. Instead, as animals breed and the populations expand, they will move from regions with higher populations to areas with lower ones.
Different species will also exhibit different tendencies when migrating. Smaller, tamer critters will congregate toward the shores of Lake Tahoe and civilization, whereas the more dangerous creatures will migrate toward the mountains away from people. The wild animals that venture too close or into the toxic mist will mutate and return to wreak havoc upon the denizens of the land.
[Source: Notorious Games press release]