Finish the game in less than two hours.
If you've already completed the original game, you probably won't have any problems with this - even if you get stuck on the puzzles and tricky walljumping.
Be sure to be as fast as possible on the shapeshifter fights. Enemies will now run towards you and trigger a fight action, so just lure the enemy to the edge when he's in Warrior form. Roll under him, then quickly push him outside. He will then shapeshift and instantly run towards you. Defeat his rush attack, then pummel him until he falls off the edge.