Complete the following achievements to unlock Xbox Live Gamerscore points.

Complete all 10 chapters to unlock Brutal mode.

Accomplish the indicated achievement to get the number of Gamerscore points:

You can buy permanent weapons from the black market guy sells. It also helps install upgrades, and allows weapons to be swapped via locker.

You can only own one type of weapon from the black market at a time. You can only change weapons buy selling the one you currently have and all its upgrades.

After unlocking the Shifting ability at the end of Chapter 7, you must sneak behind an enemy an kill him to unlock this achievement.

After unlocking the Shifting ability, you can easily kill those dangerous Elite guards by disabling all three lights from their shoulders and back, sneak up from behind then perform a fatal finisher.

Apply 5 Upgrades in the Black Market.
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Since upgrades are not interchangeable, you'll need to be very considerate when upgrading your weapons. To get this achievement early and RETAIN your upgrades, apply 5 upgrades to your weapon then reload your checkpoint after unlocking the achievement to spare your valuable upgrades from being used.

You can unlock this easily during the battle with the Colossus. Just shoot the boulders thrown at you. You can use your guns to destroy the projectiles.

You'll need to decapitate two enemies in a single glaive throw. You can target those slow moving mutants or while crossing the bridge in Chapter 4. It is recommended to steer your glaive to get a nice, clean cut.

In the later stages, you can use an ice-powered glaive to freeze falling water into solid, impenetrable pillars. Use this to create covers when approaching enemies.

After entering the church, the Colossus boss battle will begin. Acknowledge the fire across the church from you. The first tactic Colossus will use consists of him alternating the church pillars. He rips the chunks of rock from them and hurls them at you. Four shots from your pistol ought to do the trick, or you could roll out of the way using LT + A and moving the toggle stick in any direction. After dodging/shooting his throws, sprint towards the fire and throw your glaive through it. Turn around and throw the firey glaive at Colossus, who will jump to the ground ablaze. He will be stunned, so sprint towards him and perform a quick finisher. Roll to the left or right after the finishing sequence is over to dodge his counterattack. He will repeat this tactic a few other times, as will you. After a few other attempts at this, Colossus will began to emit a glowing green steam. This signals his new move. He will stay on ground level and charge at you. Roll out of the way, and use the fire pit to light him on fire via the glaive. Don't use finishers this time around. Instead, shoot him when he is on fire. Repeat a couple of times to finish Colossus.

This minor glitch happens occasionally after Chapter 5. When playing in Brutal mode, the game reverts back to normal. To avoid this, return to the main menu, highlight the Load Game option. It should say "Brutal" under the name of the current level you are playing. If it does, just continue. If not, then reload the last chapter and play it again.