If you don’t have an Energy Drainer item, the plasma pistol’s charged shot can be used to stop vehicles (but doesn’t stop vehicle mounted weapons). Pack a plasma pistol when there are vehicles around; it’s the next best thing to a rocket launcher.

You will unlock a secret achievement by finding all seven terminals listed below:

Terminals: The Ark

Go left through a door once in the very first building of the stage. The terminal is located beyond a curving passage.

A terminal is located right near the device that activates the bridge on this stage.

There’s a secret room in the third building which holds the third and final terminal on The Ark. After you come across and kill a group of sleeping Covenant enemies, head down the nearby corridor. You’ll reach a door that is locked if you do. To the left of the locked door is an open door. Head through the door, and then turn around to find the terminal.

Terminals: The Covenant

Head to the stage’s first tower and stand on the elevator. Face the control panel, and then turn left. Jump over the obstacle, and find the terminal you seek.

Head to the stage’s second tower and walk towards the entrance. When you come across a locked door, turn around to find the second of three terminals here.

Head to the stage’s third tower and stand on the elevator. Face the control panel, and then turn right. Jump over the obstacle, and find the third and final terminal on the stage.

Terminals: Halo

Traverse the first cave, and then head right until you come across a building. Walk along the passageway towards the building. Once inside, run left to find the terminal.

While collecting skulls, keep in mind that you have to start the stage from the beginning (not from a checkpoint), but once you acquire the skull you’re seeking, you can save and quit at any time without finishing the stage. This will allow you to collect skulls without having to worry about finishing the stage successfully.

To unlock the Katana, which is a non-usable item that is essentially the fourth piece of Hayabusa Armor, get all thirteen Skulls in the game, and achieve a gamerscore of 1,000 (complete all achievements).

Collecting the three pieces of the Hayabusa Armor are collected by acquiring a certain amount of Skulls in the game. To get the Chest piece, collect six Skulls. To get the Shoulders piece, collect nine Skulls. To get the Helmet piece, collect all thirteen Skulls.

Blind (Located: Sierra 117)

The arms of the player and the motion tracker disappear.

Cowbell (Located: The Ark)

Your explosives increase in strength.

Grunt Birthday Party (Located: Crow’s Nest)

If you manage to get a headshot on a Grunt, the Grunt will explode.

I Would Have Been Your Daddy (Located: The Covenant)

Unlocks new dialogue for the campaign

Black Eye (Located: Crow’s Nest)

When activated, you will have to battle enemies with melee tactics to regain shield energy.

Catch (Located: The Storm)

When activated, enemies will throw more grenades.

Famine (Located: The Ark)

When activated, dropped weapons will hold less ammunition.

Fog (Located: Floodgate)

When activated, the motion tracker disappears.

Iron (Located: Sierra 117)

When activated, you will be sent back to the beginning of the stage you’re on when you die instead of to the last checkpoint.

Mythic (Located: Halo)

When activated, all enemies will have twice as much health.

Thunderstorm (Located: The Covenant)

When activated, enemies will be of a higher rank.

Tilt (Located: Cortana)

When activated, enemies will become more resilient to your attacks.

Tough Luck (Located: Tsavo Highway)

When activated, enemies are skilled at getting away from projectiles such as grenades.

Unlock the following Elite armor permutations by fulfilling the requirement listed:

Unlock the following Spartan armor permutations by fulfilling the requirement listed:

If you beat the game on Legendary mode, you will get a special, extended ending. Keep in mind that you only have to beat the final stage on Legendary mode, and not necessarily the rest of the game, in order to unlock this ending.