Finish the game with the same partner for the majority of the journey and return to the beginning.

Sneak through the underground passage without tearing your scarf.

Kill a brute while it's charging you.

Place a cube on a button without touching the cube

Reunite with GLaDOS

Modify a weapon.

Chase down an assassin.

Start a character in multiplayer or customize a character in single-player.

Complete "Dragonslayer"

Get a skill to 100

Complete "Alduin's Wall"

Complete "Darkness Returns"

Complete 50 Misc Objectives