The following guide gives a general overview over various mercenaries within the game. They will be rated in both a PvP and PvE perspective on a scale of 1-10  (one being the lowest and ten being the highest ).

D-Class

 
Swordsman  (req. lvl: 1 ) 
Upgrades: Swordsman > Sword Fighter lv20 > Sword Warrior lv50 > Gyebaek lv80 > Hero Gyebaek lv100 
Skills: Flame sword, Dark Seed, Deadly Strike 
PvE: 8 
PvP: 6 
The basic and best tank of its class. A definite front line mercenary that wields a sword on main hand and a shield off hand. He is a melee mercenary that attacks one target and has high attack power. The swordsman has a natural fire resistance so any fire-based magic damage will be noticeably reduced when inflicted on this mercenary. Along with his shield, it makes him an ideal front line tank. However, its utility is very limited to this. Flame Sword + guarding/tanking are his primary roles. But nonetheless, it executes these roles extremely well. 

 
Spearman  (req. lvl: 1) 
Upgrades: Spearman > Spear Fighter lv20 > Spear Warrior lv50 > Zhao Yun lv80 > Hero Zhao Yun lv100 
Skills: Lightning Spear, Deadly Strike 
PvE: 8 
PvP: 7 
A melee type mercenary that uses a spear on its main hand and guardian stones  (obtainable at lv80 ) offhand. He has high physical attack power and is able to attack two mercenaries at once  (column attack ). Because of his lack of a shield and resistance to fire-based magic, he does not specialize in tanking. However, his skills truly shine when it comes to effectively draining an enemies action power  (drains two merc until the lv80 upgrade where he drains three). By draining action power, he makes it difficult for the enemy's merc inflicted by his magic to move. The ability to drain action power is something that is helpful in both PvE/PvP and his high attack power compliments this. But despite the devastating effects of his magic, the actual magical damage is fairly low. People tend to run two spears in order to maximize draining output. 

 
Archer (req. lvl: 1) 
Upgrades: Archer > Archer Ace lv20 > Archer Master lv50 > Robin Hood lv80 > Hero Robin Hood lv100 > Dark Archer lv100+quest 
Skills: Silence, Deadly Shot, Multi-Arrow @ lv100 upgrade 
PvE: 5 
PvP: 8 
A Merc that wields a bow on main hand and arrows offhand. Has extremely high attack power but lacks in survivability. She has the ability to target any merc regardless of position, which makes her excellent in sniping down opponents. Her low hp and defense makes her a second/third row merc. 
In PvE, her skills and utility aren't tide changing or unique. But in PvP, she can totally change the tide of the match. Her ability to Silence (disable skill use) is something that is feared and hinders your opponents tactics. Her single target damage in PvP is one of THE best in the game. In addition, after her lv100 upgrade, her silence skill extends an extra turn and allows you to constantly silence a targeted row. With this upgrade, she also obtains Multi-Arrow, an AOE type skill that does decent damage to enemies in the target range. 

 
Gunner (req. lvl: 1) 
Upgrades: Gunner > Gunner Ace lv20 > Sniper lv50 > Oichi lv80 > Hero Oichi lv100 
Skills: Wild Shot, Deadly Shot 
PvE: 6 
PvP: 6 
A merc that wields a gun on main hand and bullets off hand. Her attack range is three targets (column). Her ability to attack three targets at once is priceless in pvp and in pve. In lower lvls she is a definitely helpful in killing mobs and players, but it is advised to switch her out for another merc when you get access to more mercenaries as you level. 

 
Shaman (req. lvl: 10) 
Upgrades: Shaman > High Shaman lv20 > Great Shaman lv50 > Okuni lv80 > Hero Okuni lv100 
Skills: Blessing of life, Hex of Darkness, Brutal Will, Noble Sacrifice 
PvE:7 
PvP:8 
The first basic healer. She wields a staff on main hand and orb offhand. She is limited to attacking one merc only. Her blessing of life is extremely helpful in both pve and pvp as it heals three merc at once after the lv20 upgrade. However, in pvp is where she truly shines. Her unique skill, noble sacrifice, can change the tide of the match instantly. It gives a massive heal for two turns to every merc that is still alive on your team in addition to a defense boost. Within these two turns, you can do an significant amount of damage that may win you the match. But despite this life saving skill, it IS situational and can only be used when your shaman is near death (using noble sacrifice kills her as well). 

 
Monk (req. lvl: 18) 
Upgrades: Monk > High Monk lv20 > Great Monk lv50 > Dharma lv80 > Hero Dharma lv100 
skills: Awakening, Holy Guard, Protect/Shield of Protection 
PvE:7 
PvP:9 
The master of protection spells. He uses a staff on main hand and orb off hand. Attacks are limited to one merc. A Monk is almost an absolute MUST in any decent pvp build. The ability to prevent stuns and magic spells is something that is key in winning a pvp match. He does not specialize in healing or attacking, but protection and is VERY good at it. Also, protect/shield of protection gives extra protection for your main, thus increasing survivability. However, in pve, using a monk is more situational then helpful. Although, against certain mobs having a monk is indeed helpful, but it is not necessary. 

 
Viking (req. lvl: 20) 
Upgrades: Viking > Viking fighter lv20 > Viking warrior lv50 > Blue tooth lv80 > Hero blue tooth lv100 > Northern Viking lv100+quest 
Skills : Freezing Axe, Deadly Strike, Ice Ridge @ lv100 upgrade 
PvE: 8 
PvP: 8 
An axe user. Wields an axe on main hand and guardian stones( obtainable at lv80) on off hand. the viking, one of the most popular melee mercenaries, excells in his attack power and freezing ability. His attack range is limited to three mercs (row attack). In PvE, he can quickly and effectively take down mobs as well as freezing them if needed to disable their next turn. In PvP, he is generally the first to be targeted (this dictates how annoying it can be to your opponent if the viking is kept alive). His freezing disables the targeted merc next turn as well as reducing their magic def, making them more vulnerable to magical attacks. but despite his ability, he has horrid magical defense(this makes him a 'iffy' tank). Generally, he can last for a few turns, but if he is on the verge of death move him to the back row. A Viking is a fine addition for his disabling ability and attack power, but if you arent careful he can die before you can even use him. 

 
Artilleryman (req. lvl: 30) 
Upgrades: artilleryman > artillery officer lv20 > artillery captian lv50 > Napoleon lv80 > Hero Napoleon lv100 
skills: Deep insight, Deadly Shot 
PvE: 7 
PvP: 7 
The Stun king at lower levels. Wields a cannon on main hand and cannon balls offhand. His attack range is a five targets in a cross pattern anywhere within the enemies formation. In PvE, his deep insight skill is extraordinarily useful in that is reveals enemy hp and significantly reduces physical defense. This makes killing mobs a whole lot easier and faster. In PvP however, a artilleryman lacks in utility. the only purpose he will serve is adding stun pressure. The reduced defense is hardly worth it in pvp and the ability to see HP can be replaced by a license.

C-Class

 
Prophet (req. lvl: 70) 
Upgrades: Prophet > High Prophet lv20 > Great Prophet lv50 > Cassandra lv80 > Hero Cassandra lv100 
Skills: Concentrate, Broken Spear, Rusty Axe, Shattered Sword 
PvE: 9 
PvP: 7 
A highly useful mercenary in both pvp and pve if you run a fair amount of melee types in your build. A prophet wields a bow on main hand and arrows offhand. She is able to target any enemy regardless of position as well as buffing all of your melee types with accuracy, attack power, and healing. The extra attack boost is helpful in both pve and pvp, while the healing fortifies front line tanks and allows them to survive longer. For PvE, she has a variety of debuffs and significantly reduce damage from melee type mobs. The ability to target any merc also allows her excel in sniping down enemy merc. Simply put, a prophets addition to your formation can benefit both pve and pvp greatly. Her skills, although supportive, reduce damage taken as well as increasing your own damage output. 

 
Witch (req. lvl: 51) 
Upgrades: Witch > High Witch lv20 > Great Witch lv50 > Morgan Le Fey lv80> Hero Moran Le Fey lv100 
Skills: Mana Drain, Mana Trap, Mana Recharge, Meteor Strike 
PvE: 8 
PvP: 7 
One of the most unique mercenaries in the game. She wields a staff main hand and orb offhand. A witch excells in magical AOE damage with her meteor strike in both PvP and PvE. Although against some mobs it is isn't as effective due to high magical resistance, it is undeniable that she can kill most mobs effectively with one blow at lower lvls. PvP however, is a little tricky when it comes to justifying if a witch is useful or not. Her ability to levitate makes it that no physical melee damage or cannon damage may harm her. But, this is where her utility ends. She becomes merely a scroller or a one-time-use AOE caster since meteor strike makes a witch useless for 4 turns. Her limited usage makes her unappealing in pvp. 

 
Exorcist (req. lvl: 57) 
Upgrades: Exorcist > High Exorcist > Great Exorcist > Michael > Hero Michael 
Skills: Mana burn, Mana Seal, Seal Staff, Speed Cast 
PvE: 4 
PvP: 9 
A mercenary that is for pure pvp purposes. He wields a sword on main hand and guardian stones (obtainable at lv80) offhand. He has the unique ability to seal staff-using enemies regardless of position, thus preventing them from using any type of magic (a serious advantage in pvp). In PvE, an exorcist is nothing more than a meat shield. His utility and effectiveness can be replaced by almost any other mercenary, which is why he is rated at a 4 in pve. PvP however, is where an exorcist is like no other. Preventing your opponent from using protection/healing spells puts you at an advantage when it comes to stunning/disabling. Almost everyone uses a monk or healer within their formation so an Exorcist would be a necessity in pvp. 

 
Lady Knight (req. lvl: 95) 
Upgrades: Lady Knight > Royal Knight lv20 > Noble Knight lv50 > Joan of Arc lv80 > Hero Joan of Arc lv100 
Skills: Light Slash 
PvE: 9 
PvP: 7 
A direct upgrade from a swordsman. She wields a sword on main hand and shield offhand. Much like the swordsman, the lady knight specializing in tanking and single targeting. However, unlike flame sword, light slash attacks a second target with splash damage, thus inflicting around 50% more total damage. This skill makes her slightly more useful in pvp than a swordsman. Overall, her utility is limited by her ability to tank and use magical attacks. But she most definately exceeds in both these areas. 

 
Princess (req. lvl: 63) 
Upgrades: Princess > Royal Princess lv20 > Noble Princess lv50 > Isabel lv80 > Hero Isabel lv100 
Skills: Princess' Order, Royal Signet, Imperial Signet, Family Signet 
PvE: 4 
PvP: 7 
She wields a staff main hand and orb offhand. She has the ability to increase accuracy, physical defense and health of all range-type mercenaries on your team. In PvE, she is generally useless because of the fact that your frontline will be taking damage, making her health and defense buffs useless. Her accuracy buffs will usually not help in most situations due to the fact that melee damage is more than enough to finish mobs. Her signets are too situational. In PvP however, a princess is truly something to be feared if used right. Her signets can significantly reduce damage from ranged type merc, making sniping almost impossible. And since cannon/gun merc are able to bypass frontline tanks, her healing is also helpful. 

 
Oracle (req. lvl: 76) 
Upgrades: Oracle > High Oracle lv20 > Great Oracle lv50> Anck Su Namun lv80 > Anck Su Namun lv100 
Skills: Healing, Vortex, Seth's Will 
PvE: 8 
PvP: 8 
The second healing type in the game. Wields a staff main hand and orb off hand. Much like the shaman, she specializes in healing. Each of her skills are notably better than a shamans. Seth's will is almost an absolute MUST in any pve based builds. The increased damage and combo rate makes killing mobs a breeze. In PvP, her only role will be to heal and maybe cast vortex if the time is right (generally healing a row is a better choice since vortex has a two turn cool down + AP drainage). Seth's will has a lower combo rate in pvp but the ap gain and attack buff makes it a little more useful. Because an oracle does not have "noble sacrifice" she is rated at a 8 in pvp. As the end of a battle nears, healers tend to die out unless they constantly heal the row they are in. 

 
Beast Trainer (req. lvl: 44) 
Upgrades: Beast Trainer > Beast Tamer lv20 > Beast Master lv50 > Zhu Rong lv80 > Zhu Rong lv100 
Skills: Beast Summon 
PvE: 8 
PvP: 6 
The first and most basic C class type mercenary. The beast trainer wields a axe on main hand and guardian stones (obtainable at lv80) off hand. She has decent attack power and is able to target three enemies within a row. In PvE, her high defense and attack make her extremely useful. Also, her AOE skill, beast summon, is an excellent 'finishing' skill for mobs on the verge of death. In PvP however, is where she lacks. Her AOE skill deals unimpressive damage as you lvl and her only real use will be to attack the front like directly. Other mercenaries play a much better role in pvp battles and should ultimately replace the beast trainer.

 
Janissary (req. lvl: 96) 
Upgrades: Jannissary > Janissary Ace lv20 > Janissary Master lv50 > Hassen lv80 > Hero Hassen lv100 
Skills: Shooting Stance 
PvE: 8 
PvP: 7 
The highest overall damage dealer in the game. The janissary wields a gun main hand and bullets offhand. He is able to attack three targets at once in a colmn. His one skill alone makes him an absolute demon is dealing damage. Shooting stance significantly increases attack power and accuracy, making him almost always hit the targets he is aiming for. In PvE, he can quickly and effectively shoot down mobs with his insanely high damage output. This makes him the perfect merc to use in a pve rounded formation. In PvP, his damage is also something to be feared. The column damage is something that is not easy to recover from as well as adding slight stun pressure to the targets. Overall, this mercenary is almost a MUST in PvE and because of his damage, he excells in pvp as well. 

 
Inventor (req. lvl: 84) 
Upgrades: Inventor > Smart Inventor lv20 > Genius Inventor lv50 > Da vinci lv80 > Hero Da vinci lv100 
Skills: Summon Machine 
PvE: 6 
PvP: 8 
The Master of stunning. Wields a gun main hand and bullets off hand. Alone, the inventor targets three enemies. With his skill, it can potentially hit 7 targets at once. Although is damage isnt impressive, his utility lies solely in his stunning ability. With such a wide range of targets, the inventor makes stunning much more easily executable. With a number of enemy mercenaries stunned in a battle, it clearly puts you at a advantage. In PvE, he lacks in damage output. Stunning mobs generally is impossible due to the fact they are dead by the third turn. This makes his PvE role questionable as opposed to PvP where he truly shines. 

 
Cannoneer (req. lvl: 87) 
Upgrades:Cannoneer > Cannon Ace lv20 > Cannon Master lv50 > Goemon lv80 > Hero Goemon lv100 
Skills: Smoke Bomb 
PvE: 7 
PvP: 8 
The more 'pvp rounded' version of the artilleryman. The cannoneer wields a cannon main hand and cannonballs offhand. His attack range is any non-flying merc in a cross pattern. He has overall higher stats than the artilleryman but the main difference lies in their skills. Smokebomb targets all enemy targets to reduce their accuracy while adding slight damage per turn. This is extremely useful in PvP due to the fact that it reduces ALL of your opponents characters ability to attack without missing. Mercenaries rely on combo rates + accuracy in order to dish out maximum physical damage. This also helps scrolls to go off from your team, another advantage. In PvE, the same effect applies, but the effect isnt as significant as in pvp. Mobs are generally easy to kill and the accuracy debuff is, more or less, pointless. The only use the cannoneer would have in pve is his ability to target multiple targets 

B-Class

 
Elementalist (req. lvl: 100) 
Upgrades: Elementalist > High Elementalist lv20 > Great Elementalist lv50 > Pocahontas lv80 > Hero Pocahontas lv100 
Skills: Freezing Atmosphere, Blazing Earth 
PvE: 6 
PvP: 9 
The ultimate anti melee mercenary. She wields a staff on mainhand and orb offhand. The elementalist specializes in melee disabling/damaging. Freezing atmosphere seals all melee type units from using any of their magical ability regardless of position. This skill gives decent damage per turn as well as decreasing accuracy rates. Her other skill, blazing earth decreases melee Vitality and also damages per turn. With these two skills, an elementalist can effectively weaken/seal enemy tanks and other support melee merc, which is why she is ideal for a pvp based formation. In PvE, her seals and debuffs are very useful, but mobs tend to die before she is able to use her skills to the full effect, making her totally situational. 

 
Spartan (req. lvl: 100) 
Upgrades: Spartan > Elite Spartan lv20 > Spartan Captain lv50 > Leonidas lv80 > Hero Leonidas lv100 
Skills: War Cry 
PvE: 9 
PvP: 9 
One of the best defensive + offensive merc in the game. The spartan wields a spear main hand and a shield off hand. His ability to equip a shield makes him a viable tank in both PvE and PvP. Although he does not have flame resistance, his HP, Vitality, and Defense allows him to take quite a bit of damage. His skill, war cry, is useful in both PvE and PvP which is why he is rated high in both these areas. War cry significantly reduces targeted enemies combo rate (increased number of targets as you upgrade this merc), thus reducing the overall damage any mob or player can inflict on you. This does wonders when preventing scroll knock offs and controlling mobs using seth/brutal will. In addition, his offensive physical attacks deal heavy damage. And since he wields a spear, he is able to attack two mercs at once. His ability to debuff opponents/mobs as well as dishing out high damage makes him an extremely useful mercenary. 

 
Sailor (req. lvl: 100) 
Upgrades: Sailor > Pirate lv20 > Grand Pirate lv50 > Anne Bonny lv80 > Hero Anne Bonny lv100 
Skills: Toxic Sword, Blood Vengence 
PvE: 6 
PvP: 9 
The BEST single target damager in the game. The Sailor wields a sword main hand and another sword off hand (dual swords). She is limited to attack one target, but has a extremely high damage output. She aruguably has the worst survivability among all the melee mercenaries (this makes her an horrible tank compared to other mercs, so front lining a sailor must be done with caution), but her insanely high damage makes up for this. In addition, for every attack that successfully hits (excluding multi-attacks) she has a chance of activating her passive skill, toxic sword, which constantly drains AP/HP per turn. Her most powerful skill, blood vengence, does incredible damage to any target within the first two rows in the enemy's formation (this skill also damages 1/4 hp of any random character on your team, but the trade off is almost always worth it). These two skills make the sailor extremely useful in pvp. However, in pve, she is hardly worth it. Her skills are quite useless as mobs tend to die by the third turn. The only time her skills would actually be somewhat useful would be for the long and extended boss fights near endgame.

Image Credits to Stratics, Ecco, and MMO.com
Guide Credits to mindblower
Edited by Sazanality