The aliens in this game are called the Vortaak. The Vortaak attacked Earth in an earlier Godzilla game, Godzilla: Destroy All Monsters Melee (2002).
Biolante had to be cut from the game at the last minute for legal reasons.
Godzilla's roar is taken from Godzilla vs. Mechagodzilla II (1993), Godzilla 200's roar is extracted from Godzilla 2000 (1999).