Let’s not mince words
The first level brings you back to the dim streets of Dunwall, the location of the first game. Early on, you will reach a ship and speak to the captain. You then will awake in your cabin, except it’s totally weird and creepy and different. That’s because you’re actually in the ‘Void,’ the supernatural realm of the Outsider. He will offer you his mark. This grants you supernatural powers and abilities and is the standard way of playing the game.
But, woh, let’s slow down. Without any invitation, this creature hacked your very mind and transported you to his otherworldly realm. Let us remember what Lex Luthor fought for - anything that is alien and powerful must be destroyed. Okay, you can’t destroy the Outsider, but you can refuse to work with him! Tell him you’ve refused the mark and you will progress through the game with no access to either character’s supernatural abilities.
That’s right, save the empire using your wits and gadgets and not some weird occult tomfoolery. Trust what you can see! Trust what’s real!
Okay, did you refuse the mark? Are you sure? You refused?
Haha you fool! You’ve just made the game so hard on yourself. The Outsider rules. But seriously, if you do refuse the mark and play without any supernatural abilities, then you will receive the coveted and well-named ‘Flesh and Steel’ Achievement.
If you’re really looking for creating nearly impossible goals for yourself - combine this with either a Merciful or Ghost playthrough. Or both!
If you can do the triple threat you won’t get an extra Achievement but you’ll be added to my personal Dishonored hall of fame. So get to it!