At the beginning of Outskirts, jump on top of the light above the door with a crouch jump, then jump to the left platform. If you turn to your left and go down the long dark corridor, there should be a skull, pick it up. It will say blind and your screen should flash black for a while. You will not be able to see your weapon, body, shields, ammo or rader in this mode. To get rid of it, turn off your Xbox or save and quit. Go to Campaign and select level and choose Cairo Station. Skip the cinematics then save and quit. Go to Outskirt and everything should be back.
If you start on “regret,” a skull similar to the one that turns on blind mode can be found. After the first lift ride and before the first underwater elevator, grenade jump from the front awning of the lift to the ledge with the two turrets. Now, you will have to grenade jump again to the next ledge. Go to the back of the building. The skull should be there.
This is for the last level for Master Chief on Legendary. When you enter the final Gravity Lift, Look up, a skull will pass through you very fast so you must start holding X a little before you actually pass it to grab it. Once this is done, Iron mode is activated.
Grunts Birthday Mode
This can be done in Arbiter on the Legendary difficulty. Once you make it to the first banshee section, fly right away straight down all the way to the bottom of the map. There will be a circle of grunts dancing around a skull in one of the cracks where the large cylinders connect to the station. When the skull is picked up, it will say Grunt Birthday Party on the screen. Now when an enemy is killed with a projectile, they will blow up like a plamsa grenade was stuck to them. You can get rid of this the same way as you get rid of blind mode.
When you are the Master Chief trying to recover the index from the Prophet of Truth on the Covenant Holy City, go until you reach the first outdoor area with dirt and vegetation. Now go to the right as you go into the room and run up to the wall past the gravity lift that leads to the sniper point. Go up the dirt mound ad get on top of the wall. Now follow the wall and you will see the “Angry” skull.
In the big room after the armory, you will have to use a duck-jump to get onto a light fixture on the right wall (right of the room when you enter) and then jump from there to the higher area. There is a bunch of diagonal beams. Walk up one towards the end of it and use it to duck-jump onto one of the rails. Be careful not to fall between the rails. Now, walk down the rail until you can jump on the highest platform. Now bash the trashcan. It says thunderstorm when you pick it up.
In The Great Journey, it is on the top of the control room where Johnson blows up the door. When you pick this up, your shield won’t regenerate.
In Sacred Icon, there is a half-way outdoor area that has the same type of area right next to it. There is a sentinel in front of each one. Go past this area and down the piston and you will be in a very dark flood infested area. There is a bunch of boxes as you enter the room. Use them to get onto the landing above. There a few alcoves on the right side. The skull will be in the third alcove, floating above a dead human flood. This mode makes flood invincible when driving vehicles.