Suffering from a fatal blood disease, Doctor Doris Zuel sought to preserve her intellect and, after Wonder Woman was put into a coma by Neron, she attempted to transfer her life essence into the Amazon but was stopped mid-way by Wonder Girl.
Zuel’s assistant managed to save her disembodied essence, putting it into a gorilla named Giganta. Kidnapping a comatose strongwoman from the circus, Giganta transferred her essence into the woman and discovered that she possessed the mystical ability to increase in size.
Wonder Girl is captured by Giganta and Circe for a ritual of mind transference to permit Giganta an Amazonian body. She absorbs Wonder Girl's power, then attacks the player. After a bit, Wonder Girl will revive, and attack Giganta with you. Since Giganta focuses her attacks on Wonder Girl mostly, it is an easy fight.
Wonder Girl is captured by Giganta and Circe for a ritual of mind transference to permit Giganta an Amazonian body. Giganta becomes greedy and tampers with the ritual, transferring her powers to Wonder Girl rather than the other way around. It's up to newly recruited exobyte members of the Society of Super-Villains to reverse the spell and defeat Wonder Girl so that Giganta can escape!