Today, let's look at the Hexer. The Hexer hasn't changed very much from EO1, really - a couple of changes to old skills, another couple of additions... but nothing really major. None of the Hexer's abilities deal stat-based damage, so accuracy is what matters most. Debuffs hit automatically, Statuses rely on LUC to improve their chances, which leaves Revenge as the only skill that also relies on TEC to improve accuracy. However, LUC Boost won't help a great deal - take it if you really must have the maximum chance of inflicting certain statuses, but you're probably better off with more diverse skills.

Anyways, on with the skill data.

Curses
Max Level: 10. No Requirements.
Unlike most Mastery skills, Curses doesn't appear to affect anything: it's not referenced for status chances, ability speed or even Revenge's damage. As such, it seems to be purely a prerequisite for skills - nothing more. Take it as high as you need for prerequisite purposes only.

Scavenge
Max Level: 5. Reqs: L5 TP Boost, L5 TEC Boost.
This nice ability increases the drop chance of each item an enemy has. For example, with L5 Scavenge, an item with a 40% chance to drop will instead have a 81% chance to drop. Note that it doesn't matter if the Scavenger didn't get the kill or even if the Scavenger is dead: the bonus to drop rate will still be applied, and stacks with the bonuses from any other Scavengers in the party. A very useful skill, and even more powerful than it was in EO1.
L1 Stats: +1% Drop Chance
L5 Stats: +41% Drop Chance

Sapping
Max Level: 10. Reqs: L1 Curses.
Area ATK- debuff. This reduces the damage of all standard attacks by a percentage. At max level, damage will be reduced to 80% of normal. A fairly simple and useful debuff, and the fact that it's area helps much.
L1 Stats: 8 TP, 50% Spd, 98% Dmg Dealt
L5 Stats: 12 TP, 70% Spd, 90% Dmg Dealt
L10 Stats: 17 TP, 140% Spd, 80% Dmg Dealt

Frailty
Max Level: 10. Reqs: L1 Curses.
Area DEF- debuff. The targets' weakness to all six elements are multiplied by a percentage based on the level of the debuff. So if the target used to take 100% damage from Slash, they'd take 132% damage instead if affected by L10 Frailty. On top of that, if the boost in damage takes it to 110% or more, then Analysis will start working against it, granting Alchemists an even greater damage boost. L3 Frailty is enough to make a 100% Resistance vulnerable to Analysis.
L1 Stats: 8 TP, 50% Spd, Element Dmg multiplied by 105%
L5 Stats: 12 TP, 70% Spd, Element Dmg multiplied by 117%
L10 Stats: 17 TP, 140% Spd, Element Dmg multiplied by 132%

Leaden
Max Level: 10. Reqs: L1 Curses.
Area SPD- debuff. This debuff simply reduces the AGI stat of the targets, essentially decreasing their accuracy, evasion and general speed. The decrease is quite large at max level and given how important a stat AGI is, there's a high level of use available from this skill.
L1 Stats: 8 TP, 50% Spd, AGI drops to 90%
L5 Stats: 12 TP, 70% Spd, AGI drops to 80%
L10 Stats: 17 TP, 140% Spd, AGI drops to 42% 

Expose
Max Level: 5. Reqs: L10 Curses, L5 Scavenge.
Single target ELE- debuff. Unlike Frailty which multiplies the current resistances by a certain amount, Expose increases the minimum resistance allowed for that element. This occurs after Frailty's bonus has been used, so they cannot stack. This ability essentially has the effect of removing elemental resistances from a target. At L4 and above, the minimum is high enough that Analysis will now work against all elements too. This is an expensive and slow ability that only hits a single target, so you should not use this if the target doesn't resist your physical attacks already or you're already targetting weaknesses. The use of this ability is intended to aid in dealing with high resistance enemies in cases where you can't pick and choose what elements you use. Also please note that this only affects damage resistances - status resistances are naturally left untouched.
L1 Stats: 25 TP, 1% Spd, Minimum Element Dmg increases to 100%
L5 Stats: 33 TP, 5% Spd, Minimum Element Dmg increases to 120%

Cranial/Abdomen/Immobile
Max Level: 10. Reqs: L3 Curses.
Single target binds. The success rate isn't bad, but could be better. That said, binds are powerful statuses that restrict the use of certain enemy moves and can have additional effects as well: for example, Head Bind reduces accuracy, whilst Arm Bind reduces STR. If you learn which binds can restrict your opponent the most, then prioritising them can be very useful indeed.
L1 Stats: 3 TP, 50% Spd, 40% chance to bind
L5 Stats: 7 TP, 70% Spd, 50% chance to bind
L10 Stats: 12 TP, 140% Spd, 85% chance to bind

Blinding/Torpor/Evil Eye/Constrain/Corrupt
Max Level: 5. Reqs: L1, L3, L4, L5 or L6 Curses.
The above abilities (listed in the order they're learned) all work in the same way: a simple chance to inflict a status to all enemies. Other than the level they're learned at and the status they inflict, they are all identical in execution. Blinding inflicts Blind, Torpor inflicts Sleep, Evil Eye inflicts Terror, Constrain inflicts Paralyze, and Corrupt inflicts Curse. Given that the TP cost doesn't rise much but the chance to inflict the status increases rapidly, you should max out whatever you need.
L1 Stats: 6 TP, 100% Spd, 15% chance of status
L5 Stats: 10 TP, 172% Spd, 87% chance of status

Virus
Max Level: 10. Reqs: L2 Curses.
Quite powerful early on: at max level, the chance of success is very high, and the damage ignores defense. Actual damage varies by around +/-20% from the base value though. Since this is an area attack, and enemy HP doesn't go as high as it used to in EO1, it can still be useful later too. But by then, you may wish to spend your points elsewhere. Still, that's what Rest is for.
L1 Stats: 6 TP, 100% Spd, 15% chance of Poison, 25 Poison Damage per turn
L5 Stats: 10 TP, 120% Spd, 35% chance of Poison, 85 Poison Damage per turn
L10 Stats: 15 TP, 190% Spd, 105% chance of Poison, 295 Poison Damage per turn 

Suicide/Betrayal/Paralyze
Max Level: 5. Reqs: L1 Evil Eye.
These three abilities order a single enemy with the Terror status to use a particular command. Suicide causes the target to attack itself a number of times (1 to 3 times depending on level), Betrayal causes the target to attack any enemy once, and Paralyze causes the target to do nothing for the turn. Levels in these abilities only decrease TP cost, with the exception of Suicide which increaces the number of hits it makes to 2 at L3 and 3 at L5. Naturally, these abilities have no effect on an enemy that does not have the Terror status. It doesn't seem that Paralyze is all that much useful compared to the other two abilities, but I could be missing something.
L1 Stats: 10 TP, Hits self 1 time (Suicide only)
L5 Stats: 2 TP, Hits self 3 times (Suicide only)

Revenge
Max Level: 10. Reqs: L7 Curses.
A single target damaging attack. Unlike normal attack abilities, however, the base damage of Revenge is determined by the difference between the Hexer's Max HP and Current HP. Higher levels in this skill multiply this difference by higher numbers, resulting in more damage. This damage ignore defense and resistance (it counts as a Crush attack, but doesn't factor in resistance). Higher Max HP will naturally increase the damage potential of this ability. Finally, Revenge's accuracy is determined by the Hexer's TEC and LUC vs the target's AGI and LUC.
L1 Stats: 10 TP, 120% Dmg, 150% Spd, 100% Acc
L5 Stats: 14 TP, 150% Dmg, 170% Spd, 120% Acc
L10 Stats: 19 TP, 255% Dmg, 240% Spd, 190% Acc

Take
Max Level: 5. No Requirements.
No real need to go over this here.

FORCE SKILL: Curse of Ouban
A powerful area status skill that has a high chance of infliction. It attempts all statuses out of Death, Petrify, Sleep, Paralyze, Confuse, Terror, Poison, Blind, Curse and Stun. Note that except for Stun, none of the other statuses can coexist, so a priority system is used: Death > Petrify > Terror > Curse > Poison > Sleep > Confuse > Paralyze > Blind. The status that has the highest priority and also succeeds in being inflicted will be the one the target gets. This continues for all nine statuses (excluding Stun which can happen no matter what status is inflicted) and all targets. Against normal enemies, the high chance of infliction sees a large chance of Death and Petrify being seen. Against bosses and FOEs, though, their high resistance results in a more random choice of status, and their general immunity to Death and Petrify will prevent those statuses from appearing.
Stats: 500% Spd, 95% chance of status, 350 Poison Damage per turn (if poisoned)