If you've already completed Dishonored 2 and you're looking for even greater challenges, you might want to check out the recently updated Steam beta. Besides a variety of bug fixes, the full list you can find over at the Steam forums, the update has brought with it the ability to customize your difficulty through a variety of sliders.
You can adjust things such as how effective you are when leaning from behind a barrier, how quickly Sleep Darts take effect, how many active enemies are likely to attack you at the same time, and things like that. And for those of you that need an even greater challenge, there is also a brand new Iron Mode difficulty where you don't get to manually save, and where a single death will lead to a game over!
If this sounds like something you might enjoy, and you don't mind the occasional bug, you can join the Steam beta by right clicking on Dishonored 2 in your library, and then going into the betas section. But if you don't feel like dealing with bugs and glitches, or if you don't own Dishonored 2 on the PC, you can wait until January 23rd when the update will go live for all platforms. Have fun, and good luck in Iron Mode!