Unlock The Mercenaries: Operation Mad Jackal minigame
To unlock the minigame, The Mercenaries: Operation Mad Jackal, you have to bet the game once, and then save over with the 'Next Playthrough' option. Once you have done this, enter 'Load Game' and load the 'Next Playthrough'. An option will come up about what you want to load, and one of the options will be The Mercenaries.
In this minigame, you choose between Carlos, Nicholai and Mikhail to play as, and you have to get from the tram to the warehouse in a limited period of time, or you will explode. Each character has their own set of weapons and healing items. Killing enemies adds to your timer, as does rescuing hostages.
Playing this game can earn you money to spend on special infinite ammo options for the main game. Plus, it's good fun.
Okay some people may know this if they got the Versus Books guide. When you get to the part with three zombie dogs after two Hunters. Kill two of the dogs and climb up onto the stack of wooden things. Get kinda close as the dog tries to jump at you and start tapping dodge and you'll get all sorts of time and money. Then you can do it for a long time and when you get like 99:99:99 kill the little dog and run like crazy to the end XD