Posting what I found on AE forums:
Notes/How to use: DoomKnight is an excellent offensive class, hitting at 115% plus another 10% for the passive skill. Using this set of enhancements, the skill you'll want to keep going is Soul Steal. Keep stacking it 5 times as many times as you can, and once it stacks for the 5th time, wait until they stop affecting the opponent and hit the opponent with Soul Crush, dealing more damage when Dark Siphon hasn't been activated. Watch your HP, and use Void Strike whenever you feel it is necessary. This class, along with Paladin, also has a rank 10 passive. There is a .01% chance of dealing 50x your normal damage output.
Helm: Fighter / Lucky
Cape: Fighter / Lucky
Notes/How to use: Defense is indeed a possibility on the DoomKnight class. The second passive skill reduces your damage taken by 10%. Make sure you keep the Soul Steal going, as it will continue to replenish your HP. Every now and then, if you need a break from using Dark Siphon, you can use the skill Blood Offering to stun your opponent for 3 seconds.
I prefer something more solid like Fighter, but you can use full lucky or a mix.