Get nightmare mode
Complete the entire game then go to special features at the start of the game to access nightmare mode.

Get ultimate hunter mode
Finish the game once to get different costumes for your characters. To activate the extra costumes go to the option under the special features menu.

Happy ending
Rescue 50 innocents of more before you head back to the train.

Infinite Glyph Glitch
During gameplay have two players access a permanent increase Glyph (either Strength or Accuracy) at the same time and the Glyph will always be available. The regular Glyphs (Health and Conviction) are disabled on the fourth use; if one player uses a Health Glyph three times, have two people use it at the same time for the fourth time to enable the glitch.