Dark Knight: Guide by Raenryong/Job Abilities

Job Abilities
Ratings are from * (poor) to ***** (exceptional).

Blood Weapon
Notes: Normally a very ineffective two-hour ability, with a suitable Haste build and combined with Souleater, this can be the most formidable two-hour in the game. Don't rely on it to save you before then though. Notably more powerful with one-handed weapons until you can develop a proper build for it (Level 72+).
 * Obtained: Level 1
 * Enhanced by equipment: None
 * Recast: 2hrs
 * Duration: 30 seconds
 * Rating: * (with no suitable build); ***** (with suitable build)
 * Ineffective vs undead
 * Does NOT stack with weaponskills

Arcane Circle
Notes: Intimidates Arcana; Bombs, Pots, Weapons etc. Anything besides elementals which aggros to magic is a good way of remembering it. The intimidation effect can be quite handy but since this is an incredibly niche ability and even when useful doesn't do -that- much for you, I can't rate this too highly. Enhancing its duration is a nice bonus for fights like CoP Snoll Tzar, but I wouldn't say you have to carry your AF(+1) boots with you everywhere.
 * Obtained: Level 5
 * Enhanced by equipment: Chaos Sollerets, Chaos Sollerets +1; increases duration to 1:30
 * Recast: 10 minutes
 * Duration: 1 minute
 * Rating: **

Last Resort
Notes: Without Desperate Blows, Last Resort is a poor man's Berserk; increases attack by ~15% (while lowering defense by the same), lasts 1/6 of the time of Berserk AND increases your already high enmity. It is basically just a weaponskill amplifier that you must use with caution (or activate it right at the start of a battle without engaging). However, the merit trait Desperate Blows changes this; suddenly Last Resort gives 15% "faux haste" (when 3/3 merits). Now, even for general use, Last Resort puts you into a "mini-zerg" state supposing you have other haste buffs, which produces incredible DoT and weaponskill output -- a shame it still only has a 30 seconds duration! Last Resort with Desperate Blows is also insane for zerging, which will be covered later. Finally, it is up to you whether you carry around Abyss Sollerets to amplify the effect; it is not essential.
 * Obtained: Level 15
 * Enhanced by equipment: Abyss Sollerets; reduces defense loss by 10%
 * Recast: 5 minutes
 * Duration: 30 seconds
 * Rating: * (without Desperate Blows), *** (with Desperate Blows), ***** (when zerging with Desperate Blows)
 * Boosts enmity around the level of a Provoke!

Weapon Bash
Notes: Since the August 2007 update, Weapon Bash has become a potent stunning tool. It penetrates shadows which may stop other stunning methods like the spell Stun, and the stun effect lasts for a fairly long time; enough time to get Utsusemi: Ichi back up, or to buy time to your next Third Eye, depending on how you are playing. Just be mindful of the enmity gain! Finally, I would not bother with equipment which amplifies Weapon Bash damage. A ~10 damage increase or so every 5 minutes will not make a big enough difference to bother about.
 * Obtained: Level 20
 * Enhanced by equipment: There are pieces of equipment such as the Slayer's Ring which enhance the damage of this ability.
 * Recast: 5 minutes
 * Duration: Instant
 * Rating: ***
 * Boosts enmity around the level of a Provoke!

Souleater
Notes: The trademark move of the Dark Knight. Unfortunately, this ability is very commonly used badly, and "proper use" of this ability is very loosely defined and down to personal play style. Additionally, its use is very much tailored towards the situation it is in; in exp you will want to be more conservative with it, but in events it can be very powerful with the right support (which is not present in exp), especially within a zerging capacity. Many people say to use it only for weaponskills in exp, but it's all situational. If your healers are being pressured for MP, then it's emergency use only. If, on the other hand, your healers have plenty of MP to spare, feel free to use it every now and again, but communicate with your party before doing so -- they must know to expect the side-effects of Souleater. Souleater does stack with weaponskills, and weaponskills which have many hits (such as Guillotine or Rampage) will experience a phenomenal boost in damage, whilst the user's HP will also fall by a phenomenal amount. This is often tantamount to suicide, so be sure that the enemy will die in exp; in events, you often have enough support to make this more viable. Remember that a dead Dark Knight does less damage than one who isn't abusing Souleater! This is a complicated job ability, but also arguably the most powerful in the game. Use it wisely (sometimes this means not at all!), communicate with the people you are with at any given time and most importantly try not to suicide yourself with it!
 * Obtained: Level 30
 * Enhanced by Equipment: Gloom Breastplate, Sable Cuisses, Chaos Burgeonet, Chaos Burgeonet +1 and Moliones's Sickle with Moliones's Ring (set needed) all make the damage bonus 12% rather than 10%, and, do not stack.
 * Recast: 6 minutes
 * Duration: 1 minute
 * Rating: ** (in general exp), **** (intelligently used), ***** (for zerging)
 * Grants a sizable enmity bonus upon use!
 * The extra added damage is 10% (or 12% with appropriate equipment) of your current HP; therefore +HP is an important stat in a Souleater build.
 * Souleater stacks with Blood Weapon EXCEPT on weaponskills, so your weaponskills will still drain your HP.

Dark Seal
Notes: This does not enhance dark magic power, it reduces enemy resistance to the next spell. This is not so great for general use since you won't be getting many resists anyway. However, during a zerg, enemies like Kirin will resist your dark magic heavily, meaning this is your only viable way to make Drain II land. I would recommend placing only one merit in this; you shouldn't need it enough to make it ready 5 minutes faster make a difference.
 * Obtained: Level 75 (merit)
 * Recast: 15 minutes
 * Duration: 1 spell
 * Rating: * (for general use), ***** (for zergs)

Diabolic Eye
Notes: I do not like this ability. Although the +accuracy is nice, the reduction to your max HP isn't and can result in death; obviously do not use this in zergs! I would not even unlock this ability personally.
 * Obtained: Level 75 (merit)
 * Recast: 15 minutes
 * Duration: 3 minutes
 * Rating: **