1. Souleater/Darkness/Dark Wave - Old - Sacrifice HP for Damage. New - Sacrifice MP for Damage.
*Sacrificing MP seems an obvious means to maintaining the flavor of DRK without losing it's future tankyness.
Basically a modified Berserk that depletes mp. Perhaps could be synergistic with MP Refresh abilities to prolong it's duration i.e. Pots/etc.
2. Drain - Spend MP, gain portion of target's HP. No alterations needed, depending on how well it scales. Damage + Cure in a tank stance should give a nice chunk of enmity.
3. Demi/Gravity - Old - Reduces HP of all enemies to 1/4th. New - Used like flash, causing AOE Enmity and Slow/Heavy/Draw in effect for 6 seconds, dimishing returns.
4. Bio - May be a viable crossclass if SE opens it up, otherwise would likely be renamed as DRK's dark magic based DOT.
5. Death - Old - Instantly Defeat 1 enemy, sometimes fails. New - % chance on attacks that next hit will kill mob. This would be a proc effect that would effect trash mobs.
6. Blood Weapon/Sanguine Sword - Old - Drains opponents hp to heal self. New - This already exists in game somewhat as Bloodbath/Life Surge/Inner Beast. I picture this working more like Drain Samba in this game, as most other mechanics that are similar to this already exist.
7. Dark Sword & Duskblade/Night Sword & Shadow Blade - Absorbs targets HP/MP. Paladin has an ability similar to restore mp. An ideal option would be to have an HP absorb effect on the finishing combo of an enmity combo as an additional effect, or as part of a buffing combo.
8. Last Resort - Old - 15% attack buff/15% defense debuff. New - 40% Attack buff/Skill Speed Increase. The latter sounds more interesting, ends with Slow Debuff, that can be dispelled.
9. Dark Seal - Old - Boosts accuracy of next dark magic spell. New - Increases Potency of drain effects.
10. Diabolic Eye - Old - Grants Accuracy at the expense of HP. New - Sacrifices Enmity generation for increase Attack. (I.e. Default stance is Tank, this would be Sword Oath/Non-Defiance stance. Job starts with high Hp, and loses it in this stance.
11. Absorb TP - For this game, this really seems to be the most usable of the absorb spells. While it would be nice to absorb every stat imaginable, I think the number of abilities you'd take up would just be a pain and unfair to other classes.
12. Stun - Can be used like shield bash, on GCD spammable, but doesn't interupt combos. Also generates enmity.
13. Endark - Adds dark magic damage to attacks. Self explanatory.
14. Amok/Rage - Deals damage to foe repeatedly till all HP is consumed.
*I think you do need one ability that is in traditional style. I kinda picture a tether of DOT style damage that drains your HP while increasing your damage, until either you turn off the effect or the mob is dead. Perhaps something that can be negated in part by regen/stoneskin/adloquiem.
15. Minus Strike - Damage target equal to the amount of HP Lost
*if your gonna lose HP, may as well do more damage. Would be nice to sneak an off GCD ability following a Ravensbeak/Death Sentence. Timing would be everything.
16. Adversity - Physical attack, magic attack, physical defense, and magic defense each rise by 10% for three turns each time you accumulate damage equal to 25% of your maximum HP. *Seems like it could be easily modified to suit this job.
17. Draw attacks - Draw's enemy attacks onto one self. *Refer to notes on Demi)
18. Nightmare - inflicts sleep on enemies. * I picture a DOT attached to this that doesn't wake mobs, but a VERY short duration.
19. Dread Spikes - covers player in spikes for 60 seconds, draining HP from enemies who use melee attacks against player, will halt until 50% of hp is absorbed. * personally I'd like to see this as an early ability that's used the same way Rampart/Foresight is used, and have it later he buffed through progresion.
--
Also, even though this job doesn't have a scythe, a Scythe could be the magical representation for some of these moves, i.e magical non-elemental attacks that look like scythe attacks from old. Perhaps the ranged enmity move could be throwing a scythe... though seems more appropriate to make it a spell.
As for Combos, I'm fond of FFXI
Hard Slash -> Crescent Moon -> Resolution -> Enmity combo
Hard Slash -> Sickle Moon -> Sanguine Blade -> DPS Boost + Drain Samba Effect