Impossible Creatures is an RTS developed by Relic Entertainment. Its story is set in the 1930s on a fictional chain of islands. The player takes control of Rex Chance, a man in search for his long lost father and encounters the mysterious sigma technology. Sigma takes the DNA of 2 animals and lets you combine them into something new. Rex uses these new Creatures to fight the evil tyrant, Upton Julius, who murdered his father. During his missions he can obtain the DNA of up to 51 creatures. Impossible Creatures also allows you to create your own armies of 9 combined creatures outside the campaign. These can be used to fight skirmishes with AI or wreck havoc online. An additional 10 animals which are not in the campaign are available here. In addition, there is also the official, free, Insect Invasion modification, which adds another 15 creatures and many new abilities.