Dark Hunters are a combination damage dealer/disabling support class. They're, obviously, not the best at either on their own, but their base disable infliction chances aren't bad, and their damage can seriously spike when they have access to the proper skills, and have ailments/binds to capitalize on. What that does mean, however, is that Dark Hunter damage is basically RNG-reliant; if you get unlucky with infliction rolls, or even recovery rolls, you're going to be left with a somewhat-fragile party member that doesn't deal fantastic damage. They're best paired with a Hexer, as you might infer, since Hexers are custom-built for inflicting ailments and binds.

Stats

(Full stat table)

Common Passives: ATK Up, HP Up, TP Up
Gathering Skill: Take

Dark Hunters have above-average stats as far as STR, TEC, VIT go, okay LUC, and very good AGI. Their HP's less than optimal, but not bad by any means. Their TP is annoyingly low, but you're going to be casting their basic skills more than their big damage skills (obviously), so it's not too limiting.


Whip Mastery


Needed to learn whip skills. Increases damage dealt with whips.

Gag / Cuffs / Shackles


Deals melee STR-based cut damage to one enemy. Attempts to bind the target's head (Gag), arms (Cuffs), or legs (Shackles). Has a 90% speed modifier and a base accuracy of 108% at all levels.
The basic whip skills are the core of the whip skill tree, and you will need all three of them maxed out eventually. They don't deal fantastic damage--in fact, I wouldn't even say they deal okay damage--but it's either them or nothing, really. What're you going to do, use an attack skill, via a Grimoire, that doesn't inflict binds? That's just silly.
These things cost a lot, relatively speaking, for not very amazing damage. The compensation is that the base infliction rates are pretty high, I suppose. I'd still have a Hexer or a specialized party composition prepared to assist with binding for more efficient turn economy to set up for Ecstasy.

Ecstasy


Deals melee STR-based cut damage to one enemy. The damage is altered based on the number of binds the target has. Has a 90% speed modifier and a base accuracy of 98% at all levels.
EOU Ecstasy's nowhere near as overpowered as the EO2U version, and contains a bizarre bug, but it's still the Big Damage Option for whip DHs. I say "nowhere near as overpowered" for two reasons: inflicting multiple binds is way harder without a Creeping Curse Hexer for backup, and you don't have passives like Curb ATK Up to help with the Dark Hunter's own infliction rates this time. Ecstasy also just overall deals less damage but that's not as big a problem as you'd think, since enemy HP totals are way lower in EOU than EO2U.

Huh, what, say something about Ecstasy on its own? Okay, sure, it's the skill you use when an enemy has a bunch of binds and it lets Dark Hunters actually deal damage for a bit.
It's not as good as EO2U's due to metagame, but it still hits like a goddamn truck if you manage to get it to land with high bind amounts. It just requires a more specialized setup instead of "I used Stigmata and won".

Viper


Deals melee STR-based cut damage to one enemy. Attempts to inflict poison on the target. Has a 90% speed modifier and a base accuracy of 98% at all levels.
The only whip skill that inflicts an ailment, and it's far more broken than it looks. See that 650 base poison damage? At 11 TEC, which a DH will have around the first boss, it will tick for 725 to 740 damage. The first boss has 3372 HP, and 100% vulnerability to poison. The second boss isn't much better off, with the same vulnerability and 6880 HP. Past that, poison doesn't scale quite quickly enough for Viper to be as impressive, but it's still the strongest poison skill in the game.
The main drawback is Viper's unimpressive TP cost, which Dark Hunter can't quite keep up with, especially at low levels. Besides that, yeah, a Lv.15 Viper can do some serious tick damage.

Climax


Targets one enemy. If that enemy is at 40% HP or below, attempts to instantly empty their remaining HP--this chance is affected by the enemy's vulnerability to instant death. If the HP emptying succeeds, restores a percentage of the HP emptied to the user.

Climax does not count as instant death, and will not give instant death conditionals. Does not work on bosses.

Has a 90% speed modifier and a base accuracy of 98% at all levels.
Uh. What?
The removal of Climax's Death property is really awful, and it makes getting a few particular drops utterly insufferable due to EOU's poor assortment of Death skills. Besides that, it's okay for dealing with meatier FOEs if your burst isn't up to snuff.

Sword Mastery
Requirements: None


Needed to learn sword skills. Increases damage dealt with swords.

Hypno Bite / Nerve Bite / Mirage Bite


Deals melee STR-based cut damage to one enemy. Attempts to inflict sleep (Hypno Bite), paralysis (Nerve Bite), or panic (Mirage Bite). Has an 80% speed modifier and a base accuracy of 98% at all levels.
Same deal as the basic whip skills. Having access to sleep, paralysis, and panic is actually a fairly big asset in sword DHs' favor, since all of them are debilitating ailments with quite a few uses.
These have pretty good infliction rates and Nerve Bite is one of the few reliable sources for paralysis in a player-based toolkit. However, the TP costs on these can run a Dark Hunter dry fairly quickly if spammed and you don't get the skill that capitalizes on ailments until heavy investments are made. I'd suggest having a Raging Edge grimoire laying around for them to use for the early game, if possible.

Soul Liberator


Deals melee STR-based cut damage to one enemy. If the target has an ailment, Soul Liberator's damage is quadrupled, and the ailment is dispelled from the target. Has an 80% speed modifier and a base accuracy of 98% at all levels.
Soul Liberator's an interesting contrast to Ecstasy--it's far easier to set up and deals way more damage up until the 5th Stratum or so. On the other hand, if you have a strat that relies on using ailments to weaken FOEs/bosses, Soul Liberator's going to be an active detriment to you, since it immediately dispels ailments.
I'm a real big fan of Soul Liberator. It favors single-turn intense bursting, and it synergizes well with things like Muting Word on Hexer. It can take a while for your Dark Hunter to get to the point where they can reliably use this without TP exhausting themselves on other attacks, though.

Drain Bite


Deals melee STR-based cut damage to one enemy. Restores the user's HP for a percentage of the damage dealt. Has an 80% speed modifier and a base accuracy of 98% at all levels.
Blehhhhhhh. Garbage damage, and I don't really believe DHs need to self-heal that much.
Mediocre damage for way too much TP for doing something that actually actively hinders Dark Hunter if you're min-maxing. Not recommended.

Catastrophe


Deals melee STR-based cut damage to one enemy. Attempts to inflict petrification on the target. If the petrification fails, increases the user's chance of inflicting ailments and binds for one turn. Has an 80% speed modifier and a base accuracy of 98% at all levels.
Not as useless as Climax, mostly because every boss has 1% vulnerability to petrification, meaning that infliction is basically never going to actually proc, turning Catastrophe into a ailment/bind chance booster that deals some damage. It's not cheap in terms of TP cost, mind you, but then again, what powerful skill is?
This is a fairly decent skill for dealing with difficulties for infliction, and petrification can be useful for problematic enemies. That TP cost hurts, though. At least the damage is nice.

Boost Up


Increases the user's Boost gain.
Basically every DH skill benefits heavily from Boost (the basic whip/sword skills get buffed base infliction chances, Ecstasy and Soul Liberator deal a bit more damage, and Catastrophe gets a pretty serious infliction chance multiplier boost), so hey, why not make it available more often?
Honestly, this is a really good skill to have on Grimoire Stones for anyone. More Lv.15 skills is really good.

Wrath's Might


Increases the user's damage when they are below a certain HP threshold.
Wrath's Might is a serious gamble. Dark Hunters aren't as fragile as certain other classes, but leaving one at 50% HP or lower all the time is going to get them killed very quickly. Whether or not you invest in it is up entirely to your party composition. Shadow Veil can help, I suppose.
Behold, the territory of the min-maxer! This skill is goddamned incredible, but the real challenge is keeping your attackers with it on their feet. If you're really going for broke you can have this on Grimoire Stones for them.

Bait


When the user or an adjacent party member are attacked with physical damage, the user will retaliate with melee STR-based cut damage to the damage source. The damage is increased if the user is countering an attack to themself. Each time Bait activates, the chance of it activating again on that turn is decreased. Bait has a maximum amount of times it can activate on one turn. Has a base accuracy of 98% at all levels.
Blehhhhhhhhh no thanks. The damage numbers on Bait just aren't high enough for it to be worth it.
EO2 this ain't. Nerfing ally damage really put a damper on the efficacy of this skill. There's a few applications I can think of for this, but most of them would just end up with relatively underwhelming damage. Or just a very dead Dark Hunter.

Bind Heart


Reduces one enemy's speed for a set amount of turns. Has no speed modifier at all levels.
Ew.
This skill gets pretty significant, but there's probably only one encounter where speed is a true critical factor and it's honestly tolerable without any modifiers. This skill is sadly situational to a fault.

Shadow Veil


Reduces the user's chance of being targeted by enemies for a set amount of turns. Has no speed modifier at all levels.
This is one way to keep a DH taking advantage of Wrath's Might alive, but it's not particularly reliable, and does require wasting turns to set it up/keep it up.
This requires a setup turn, and while it looks nice initially it's still not going to save your Dark Hunter from any sort of area of effect attacks, of which there are plenty in this game.

Dark Curse


Attempts to inflict curse on all enemies. Has no speed modifier at all levels.
lol
Curse, please go away. I don't like you.