Training challenges:
Win the game in tournament mode to unlock all training challenges.

Minotaur and Scorpius:
Successfully complete the game in tournament mode under the advanced difficulty setting.

Sallus and Agrippa:
Win the game in the tournament and academy modes.

Germania team:
Successfully complete the Germania level in tournament mode under the advanced difficulty setting .

Egyptian team:
Successfully complete the Alexandria level in tournament mode under the advanced difficulty setting.

ADDED BY DJB (Cant tell the difference)

Get Minotaur & Scorpius:
Use advanced difficulty and finish the game in tournament mode

Get Sallus & Agrippa:
Finish the game with tournament & academy mode

Get All training Challenges:
Finish the game with tournament mode