Some characters (such as Experiment 626, Prince Phillip, and Mickey) occasionally fight alongside the player characters in battles as partners similar to the other games, providing assistance and performing combos to help the player proceed. However, they do not follow the player around constantly like Donald and Goofy in the other games. Unlike the other major installments, which also featured casts of various characters throughout the Final Fantasy series, Birth by Sleep only features two of these characters: Zack Fair from Final Fantasy VII, and the Moogles, creatures from several of the Final Fantasy games, who sell items to the player.[23] As Birth by Sleep is a prequel of the first Kingdom Hearts title, the staff decided to add Zack to the title as he is the protagonist of the Final Fantasy VII prequel, Crisis Core: Final Fantasy VII.[19]