Onslaught Cheats

Extra Difficulties
In addition to the three difficulty settings available from the start, there are two unlockable difficulty settings.

Expert difficulty: Finish the game on Hard difficulty
Ultra difficulty: Finish the game on Expert difficulty

Upgrade Locations
Each weapon (including grenades and the whip) has 2 upgrades that count as additional weapons. The upgrades carry over even if you start a new game on another difficulty (on the same save spot):

2nd level Assault Rifle: Box in Mission 5
2nd level Grenades: Clear Missions 1, 2 and 3 in Normal difficulty (S rank)
2nd level Rocket Launcher: Clear Missions 9, 10 and 11 in Normal difficulty (S rank)
2nd level Shotgun: Box in Mission 11
2nd level SMG: Box in Mission 3
2nd level Whip: Clear Missions 5, 6 and 7 in Normal difficulty (S rank)
3rd level Assault Rifle: Beat the game in Ultra difficulty
3rd level Grenades: Clear Missions from 1 to 8 in Hard difficulty (S rank)
3rd level Rocket Launcher: Clear Missions from 1 to 12 in Ultra difficulty (S rank)
3rd level Shotgun: Beat the game in Expert difficulty
3rd level SMG: Beat the game in Hard difficulty
3rd level Whip: Clear Missions from 1 to 8 in Expert difficulty (S rank)