Recruit Selene quest guide has been updated.

Darkness v9.11

In v9.11.0, [Darkness] debuffs will be revised. See 뜨거운 감자 다크니스, 드디어 변화가 시작된다! for details. The article uses L12 [Deep Sleep] (110% base chance) as a testing skill. The changes are as follow: 
  1. Intelligence (INT) of caster will affect debuff probability. For example, a wizard with INT 70 will have a total chance of 110 * 70 / 100 = 77%. 
  2.  Buffs that resist debuffs will also affect debuff probability. For example, if the target has 20% debuff resistance, the chance will be (110-20) * 110 / 100 = 99%.
  3. All characters with [Darkness] stance will have their ability statistics reset. 

Characters & Statistics
So what does this mean for the various characters and their statistics builds?

Character INT CON Debuff Max HP
M'Boma 70 90 77% 70,940
M'Boma 100 60 110% 55,970
Emilia the Sage 80 70 88% 58,916
Emilia the Sage 110 40 121% 46,055
Wizard 70 70 77% 60,230
Wizard 100 40 110% 46,915

The Max HP listed above is based on Master Lv.10 with Family Lv.41, using maximum-HP enchanted Crafted Necklace, Magic Earrings, Magic Belt, Magic Gloves, Magic Shoes, Custom Wings, Enhanced [Darkness] Rings, Boost Potion, L12 [Principal], and L12 [Strategy] (aka [Melee Enhancement]).

All characters gain +33% debuff chance when INT increases by 30 points, while max HP drops by approximately 13,000 to 15,000. As such, [Darkness] users should invest in INT after v9.11.0 update. Note that Emilia the Sage mentioned here is the original one with base INT 80, and not "Emilia the Sage 2" released for Singapore edition with base INT 70.

[Darkness] vs. Resistance
Debuff resistance will lower debuff chance. The following test is based on M'Boma against a target with [Rouse] (aka [Escape Artist]; L11 resist 11% for 16.5 seconds) and/or [Ignore Harm] (L10 resist 50% for 240 seconds).

Caster Rouse Lv. Ignore Harm Lv. Debuff
INT 74 - - 81%
INT 104 - - 114%
INT 104 11 - 103%
INT 104 - 10 62%
INT 104 11 10 51%

Note that [Redemption], [Wanted Action], and [Frost Shield] skills also grant complete debuff immunity for a few seconds. The following graph shows Emilia the Sage (INT 110) against the various resistances.

Note that INT can be boosted further with necklace (+3), belt (+3), rings (+4), earrings (+3), and Status Ampule (+3). One item of note is Will of Argus (earring) which grants INT +10.

Why Use Emilia the Sage?
Highest chance to debuff due to base INT (80)
Access to [Enhanced Tactics] stance in v8.10.0
Access to [Incantation] stance to resist enemy debuffs
Role: Debuff + Buff

Why Use M'Boma?
L11 Power of Absinia: More HP, DEF Rating +1 for 20 seconds
Highest HP due to base CON (60)
Role: Debuff + "Tank" (sort of...)

Why Use Wizard?
L11 Energy Shield: Absorb damage, DEF Rating +1 for 58 seconds
Access to [Telekinesis] stance to deal noteworthy damage
Access to [Incantation] stance to resist enemy debuffs
Role: Debuff + Damage

...What About Normal Emilia?
Normal Emilia is not mentioned in the article, but she has base INT 60, so she is even worse than M'Boma when it comes to inflicting debuffs. She should probably stick to CON build instead. That way, she can function as a scout buffer with bonus magic buffs and reasonable HP. If she uses INT build instead, she is going to be out-matched by Emilia the Sage. [Whole Cancellation] should be still useful for her though. So her role is better suited as a scout replacement.

Additional v9.11.0 Patch Notes
  1. Each Master level grants bonus HP equals to (CON * CON / 7.5) + 500.
  2. Movement speed limit has been improved. [Madness] stance can allow even faster movement.
  3. RES penalty for INT 50 or less has been removed.
There are also 2 articles you may want to read up on - Revised Arsene's Secret Vault v9.10.1 and Revised Secret Tower v9.9.1. I may or may not translate them, depending on how much free time (and motivation) I have available.