Devil May Cry (PS2)

Unlock Dante Must Die Mode
Beating the game on the Legendary Dark Knight Mode will unlock this mode.

Unlock Easy Difficulty
Easy Mode will unlock if you use an excessive amount of continues in the first few levels of the game. Basically, the more you die, the greater your chances of unlocking the Easy Difficulty setting.

Unlock All-Star Group image
On every mission, get a rank of S.

Recharge life and Devil Trigger
To recharge your Devil Trigger, go up to an enemy (close enough so that your vitality bar appears) and press R2 to taunt it (with a sort of Just Bring It! style taunt). This will raise half a block of your Devil Trigger each time so once you get 3 or more, you can use Devil Trigger to regain some life then do it again.

This really helps on your first encounter with Nelo Angelo. Once he teleports the first time (and does a taunt) go up to the crack in the wall below where he is waiting and press R2 to raise some DT.

Note: Once you press R2, you are completely defenceless and cannot attack or move until Dante has finished the taunt. You've been warned...