Oldschool Tyris costume:
To unlock the Oldschool Tyris costume, successfully complete the game.
To unlock Challenge mode, successfully complete the game. Start a new game and select "Challenge mode" at the start to play with your previously unlocked costumes and weapons.
Unlock the following costumes by successfully completing the corresponding levels:
COSTUME - HOW TO UNLOCK
Undead Scout costume - Queen of the Dead
Wastelands Scout costume - Secondborn
"The Classic Look" costume - Death Adder
Diyar Tracker costume - Firstborn
Fiend's Battle Path Armor costume - The Last Titan
To unlock Brutal difficulty, successfully complete Story Mode.