These are the tasks you have to fulfill in order get them

Unlockable	How to Unlock
"The Emperor" Mateus	Buy him for 500 PP in the shop
Cloud of Darkness	Buy her for 500 PP in the shop
Exdeath	Buy him for 500 PP in the shop
Gabranth	Complete his story mode. Then buy him for 1000 PP in the shop.
Garland	Buy him for 500 PP in the shop
Golbez	Buy him for 500 PP in the shop
Jecht	Buy him for 500 PP in the shop
Kefka	Buy him for 500 PP in the shop
Kuja	Buy him for 500 PP in the shop
Sephiroth	Buy him for 500 PP in the shop
Shantoto	Complete her story mode. Then buy her for 1000 PP in the shop.
Ultimecia	Buy her for 500 PP in the shop