Select the Endless gametype from the main menu.

Character	How to unlock
C.Zero	Defeat him in Endless mode battle No.63 or in story mode
EX Robert	Defeat him in Endless mode battle No.10 or in story mode
Geese	Defeat him in Endless mode battle No.59
Goenitz	Defeat him in Endless mode battle No.60
Igniz	Defeat him in Endless mode battle No.65 or in story mode
Krizalid	Defeat him in Endless mode battle No.62 or in story mode
Rugal	Defeat him in Endless mode battle No.66 or in story mode
Zero	Defeat him in Endless mode battle No.64 or in story mode