The King of Fighters XI Cheats

Random Select
Press [Start] + [any direction] on any character select screen:

Press [Start] + [Up] or [Down] when choosing a character: Random (single) - choose a single random character
Press [Start] + [Left] or [Right] before choosing any characters: Random (team) - choose a random team of characters

Choose Who Challenges You in Stage 4
On stage 4 in arcade mode, you will get challenged by a secret character. The character that challenges you is determined by how many LDM you land on your opponent before that, you will get at most 2 LDM usage per stage, so to fight Jyazu or Silber, you must land all 6. If you meet the requirement for Jyazu and Silber, the one who challenges you will be random between these 2. This will help you unlock these character faster.

Adelheid: Fail any of the requirements.
Gai: KO at least 1 character with a LDM.
Jyazu: KO at least 6 characters with a DM, use at least 2 LDM in the fights. No teamates may die.
Sho Hayate: KO at least 3 characters with a LDM, no teamates may die.
Silver: KO at least 6 characters with a DM, use at least 2 LDM in the fights. No teamates may die.

Unlock all the characters
Adelheid: Defeat him in arcade mode when he challenges you.
Ex Kyo Kusanagi: Complete Challenge number 30.
Gai: Defeat him in arcade mode when he challenges you.
Geese Howard: Complete Challenge number 40.
Hotaru Futaba: Complete Challenge number 15.
Jyazu: Defeat him in arcade mode when he challenges you.
Magaki: Complete Challenge number 6.
Mai Shiranui: Complete Challenge number 20.
Mr. Big: Complete Challenge number 35.
Robert Garcia: Complete Challenge number 10.
Shion: Defeat her in arcade mode. She is the fight befoer Magaki.
Sho: Defeat him in arcade mode when he challenges you.
Silber: Defeat him in arcade mode when he challenges you.
Tung Fu Rue: Complete Challenge number 25