Dark Knight: Guide by Raenryong/Merits

This is personally what I think you should merit on Dark Knight, although it is obviously the setup I use and you may find that you like things which I don't!
Attribute Merits:
Some combination of HP and MP depending on whether you use DRK purely for zerging or for more general uses.
STR: 5/5
Combat Merits:
Scythe and/or Great Sword: 8/8
Magic Merits:
Dark Magic: 8/8
Group 1:
Last Resort Recast: 5/5
Last Resort Effect: 5/5
Group 2:

Due to recent changes, it is difficult to decide what to do with this category.
Desperate Blows is very powerful in a variety of situations, whereas Dark Seal is very situational. Diabolic Eye only becomes good when it has a low recast (lots of merits), and Muted Soul is situational.
For an all-purpose Dark Knight, I would recommend 1x Dark Seal, 4 or 5x Desperate Blows and 5 or 4x Diabolic Eye. If you do not intend to zerg, I recommend 5x Desperate Blows and 5x Diabolic Eye.

This gives you a powerful build and enhances Last Resort to the stage it can be used every 4 minutes 10 seconds, with the +ATK (also the -DEF!) of a Berserk but also with the added "faux haste" effect. Dark Magic merits are handy since Dark Magic is based almost solely on Dark Magic skill, and combat merits give you more "base accuracy", allowing you to build for haste/meat a lot easier.