What do the Campaign system settings ("Attack Reaction", "Infinite Ammo", "Agent Hunt Settings") do?

Solution 1:

I share your pain regarding the lack of a manual, or in-game guide! Having to learn all the controls by trial and error (with no real break in the action) is very frustrating. :(

Infinite ammo will probably be done like in 5; that is, once you unlock infinite ammo, you will have the option of turning it on or off...but you have to get the ability first.

Attack reaction is probably whether or not your partner reacts (stumbles, trips, etc.) if you hit them with your own attacks. They probably won't take damage, but hitting or shooting them will throw them off a little. Again, like in 5.

"Agent Hunt" is one of the new minigames (like The Mercenaries), and I have no idea about it yet.

Solution 2:

Attack Reaction

Toggles "friendly fire" (you and your partner flinch and react to being in the other's line of fire, and take some damage accordingly).

Infinite Ammo

Doesn't do anything until you purchase the unlock from the skill point store (available after finishing all four campaigns, each weapon's infinite ammo costs 80k points separately). This toggles whether those purchases are active.

Agent Hunt Settings

Allows other people to join your game in Agent Hunt mode (available after finishing any one campaign), where they play as a zombie and attempt to kill you. (NB: The controls are horrible.)

Solution 3:

The Agent Hunt is actually a mini-game that allow you to play the role of a monster on another player's game (if the player allows it). I didn't test it yet, but judging by the description it could be cool once you finished the game and got everything already.