Boss Rush Mode
To unlock Boss Rush Mode, have a gamesave of Metal Gear Solid Portable Ops on your memory stick, then start a new game with it.
Character Passwords
Enter the password in the "Recruit" "Password" section of the main ingame menu.
Password - Result
TTOGZWSREYD - Arms Magazine Soldier
Ground hold up position
If you find yourself in trouble or just on a special mission with either a constant Alert phase or a neutralize enemies objective, throw them down and point the gun at them to make them "Freeze". This will force them to go into the ground hold up position. This approach is recommended, as you do not need lots bullets to force your way through the stage. Also, if the Alert phase clears you can see how many stars the soldier has to deem whether or not you wish to recruit them to your cause. From there you can leave them and continue, knock them out for items, recruit, or try the next trick. Note: A stage can only play host to a certain number of soldiers; if all the soldiers stationed there are alive, no more can come out to shoot you. This is perfect if you want to recruit just a certain soldier type on a constant alert map. Also if there is a wandering soldier in the Evasion (orange) or Caution (yellow) phase that spots your subdued enemy, they will be brought back to their feet and the Caution phase will be brought up or reset. Finally, if you have a large number of soldiers held up like this, make sure you do not fire your gun on empty. They may just get angry with you.
Johnny
Find Johnny from Metal Gear Solid, Metal Gear Solid 2, and Metal Gear Solid 3 as a random prisoner in Infinity Mission.
Standing hold up postion
This may require some effort with the "punch punch kick" combo, but it may be easier with a rifle or SMG. When an enemy is prone on the ground in the hold up posture, move toward the torso. After the kick or swing of your weapon, immediately press X to crouch. If done correctly, both characters will flinch and the enemy will be now be standing in the hold up posture. This is much easier than knocking them out to shake them or then waking them up just to hold them up again.
Taunts
Find all 68 entries on the soldier list, then complete an Infinity Mission round to unlock all sixteen taunts.
Tengu Soldier
To unlock the Tengu Soldier, play on any difficulty level (normal or above). Knock out the first Tengu Soldier you come across and carry him back to the truck unconscious. This will allow you to play as him.
Unlock Naked Snake
Beat easy mode in infinity mission.
Unlock Old Snake
Beat Medium mode in infinity mission.
Unlock Raiden
Beat hard mode in infinity mission.
Unlock Roy Cambell
Beat extreme in infinity mission.