Sniper rifle range mini-game:
Successfully complete Campaign 1 to unlock the Sniper Rifle Range mini-game.
EMP Cannon Range mini-game:
Successfully complete Campaign 2 to unlock the EMP Cannon Range mini-game.
Cow Bouncing mini-game:
Successfully complete Campaign 3 to unlock the Cow Bouncing mini-game.
Assassination mini-game:
Successfully complete Campaign 4 to unlock the assassination mini-game.