Any creature, object, event, etc that is not native to the reality with the potential to corrupt the world around them. Alienation can stem from Aberrant creatures similar to being directly exposed to the Chaosphere/Dark Energy Network itself.
Truetopia is filled with a veritable collection of aberrations and monstrosities. These beings are often what is warned about by the West Village Council and the Cult of the Elders, as it was unheard of for villagers to survive beyond the walls at night, due to such creatures.