They each allow you to obtain different materials for creating weapons and armor, which you in turn obtain from hunting various beasts on missions. (thekoalition.com)
Sidequests (See: hunts) were also opened up, and I was plopped into a fucking massive field filled with various beasts and a pretty spectacular view. (riddlethos.com)
Altered Beast — Summoned from the dead by Zeus, players in Altered Beast must shape shift into various beasts and fight off hordes of demons to rescue the captured Athena from the clutches of Neff. (darkainarts.com)