A highly complex, but generally hidden system added by the AvP : Humans module is the Genetics System. This system allows players to take the genes from mobs and apply them to other mobs. Through this, players can get uniquely producing modified mobs such as a slime that drops leather upon being killed.
This system also ties in with the AvP : Aliens Module. Through this, Aberrants are created alongside intense integration with strains, leaking and more.