Dark Avenger aka Hell Knight lineage gracia

The Dark Avenger (DA) is a hybrid summoner-tank. Mostly tank, partly summoner, the Dark Avenger has a drain of the same power as other magic skills. Of course, having no M. Atk passive skills leaves his drain relatively weak, but useful nonetheless. They retain their level 35 self heal, but even with Blessed Spiritshots, it tends to just make you an arrow/nuke magnet. The Dark Avenger’s main draw point is its summon: the Dark Panther. Once feared universally, in the current age of archers and nukers with soulshots, spiritshots, outrageous casting speed, the Dark Panther has fallen by the wayside. Thanks to Chronicle 4’s improvements to the summoning system, summons once again pose a significant threat. The human tank’s Shield Stun is the only non-force stun in the game, and has the highest land rate of all stuns in the game. In PvE, the stun will sustain about 5 hits (by anyone) on average before breaking, but in PvP, you can rely on it to only survive about 1 to 3. Majesty, the human tank’s unique self buf, increases our P. Def again at the same rate as Shield 3, but at the cost of 8 Evasion. Even little level 52 daggers will be able to hit you, so get ready.
The DA has other skills of importance, including Hamstring and his life drain. To M. Def-resist people your level, expect your drain to do no more than a few hundred damage. You might be able to do double to low M. Def or badly jeweled enemies, and much more to lower level enemies. Hamstring, the bane of all archers and nukers, is in the arsenal of the DA, and one of his most important weapons. A slowed enemy is a dead enemy. DAs who forget this important skill are really reducing their chances in PVP; both their own and their side’s.
In PVE, you can’t really go wrong picking a DA to tank for your group. They’re the only pure tank that doesn’t get 360 degree shield blocking of any kind, so the DA must either rely on his skill or luck to keep his shield between him and the gobs of mobs. They generally have tons of HP, like Paladins, but they do not have any undead passive skills. Instead, they have Corpse Plague and Corpse Drain, which if managed properly can add a some extra uptime to your party. The Corpse Drain returns about 100 HP + 10* skill level per corpse for a light a-beep-t of mana…not enough to solo on, but enough to help in a small group. Corpse Plague is really just a novelty at higher levels; the DA’s low M. Atk and infrequent levels of the Corpse Plague skill make it unlikely to land on mobs your level.
In PvP, the DA was once king of the hill. The DA as of now still packs a decent punch, but not what it used to. Being a hybrid summoner-tank, expect to play that way in most PvP’s: as support for your panther. A Dark Avenger’s most conventional attack strategy is to stun their opponent, Hamstring (slow) them, and drain them while their panther does most of the damage. HP weapons are common and some say most preferred. The PvP style of a Dark Avenger relies heavily upon his panther, and his ranged slow, Hamstring. The Dark Panther is extremely annoying to anyone not attacking it, deadly to those who ignore it. The second the panther is targeted though, it’s just another mob: dropped in three to six hits from ranged DD ’s, about double from melee DD’s. He’s got high P. Atk, HP, and base run speed, but it has low P. Def, M. Def and critical rate, even buffed. Even with those disabilities, the panther can really do some serious damage to an enemy (especially with pet soulshots). Some DAs have foregone their HP heritage and set themselves up similar to the Paladin Damage Dealer, but this trend doesn’t seem as common among DAs as it is Paladins.
High level Dark Avengers get skills to help them in fighting melee DD's: Shield Slam, which interrupts physical skills, and for everyone, disarms them. They also get Physical Mirror, a buff that reflects Melee debuffs back on the caster. Unlike the Paladin and the TK, the Dark Avenger’s dark nature lets him learn an ultimate curse: Touch of Death. By sacrificing 1338 HP, it significantly decreases a target’s maximum CP for a brief time period and decreases resistance to debuff attack, and the effect of HP regeneration magic. However, it's limited in that it can only be used at less than 75% HP. They also get another Ultimate Defense that causes people to change their target to the Dark Avenger. Like all other tanks, DAs get passives to resist poison, bleeding, sleep, and holds. Most importantly, they get a toggle that greatly increases their resistance to stun and paralysis. Also, Paladins get a self buff, Physical Mirror, which acts like Magic Mirror, except reflecting debuffs caused by physical attacks. These together will give human tanks a distinct advantage against classes that rely on physical attacks.

Playstyle
Tanks are obviously quite easy to solo. In the case of the Dark Avenger, he can even gain support from a summon.
Inside groups, they activate their Hate Aura and keep mobs attacking them instead of the damage dealers.
Best group for a tank is of course a mix of buffers, a large number of damage dealers and nukers, and maybe a healer. Best buffer for the tank himself is a Prophet who avoids buffing 'Berserker Spirit' to the tank, plus an Elven Elder - because of their Agility buff, but they can also give mana and healing and raise almost as good as a Bishop - and a Swordsinger. Of course the other party members will prefer other buffer classes which optimize offense instead of defense. Most anoying for the tank is probably an Overlord because they buff Berzerker Spirit - on everyone of the alliance, so you don't even have to be in party with the Overlord to receive this buff.
Skills
Active

Aggression (lvl 49) - Provokes your opponent into attacking.

Aura of Hate (lvl 37) - Provokes your opponent to attack.

Banish Seraph (lvl 74) - Strikes fear into an angel, causing it to flee. Lethal Strike is possible. Consumes 10 Soul Ore.

Corpse Plague (lvl 4) - Corpse emits a cloud that poisons nearby enemies. Instantly poisons nearby enemies.

Deflect Arrow (lvl 4) - Temporarily increases defense against bow and crossbow attacks.

Divine Heal (lvl 9) - Recovers one's HP.

Drain Health (lvl 53) - Absorb the target's HP. Power 108

Fortitude (lvl 1) - Increases resistance to Shock/Paralysis attacks significantly. Continuously consumes MP.

Hamstring (lvl 14) - Instantly reduces enemy's Speed.

Horror (lvl 13) - Instills fear into an enemy causing it to flee.

Iron Will (lvl 3) - Temporarily increases M. Def.

Judgment (lv 10) - Uses your collected dark energy to provoke an enemy to attack while temporarily decreasing their critical attack power. Requires a sword, blunt weapon, or dual-sword weapon. Over-hit is possible.

Life Scavenge (lvl 15) - Drains HP from corpses and uses it to restore your HP.

Majesty (lvl 3) - Temporarily decreases Evasion and increases P. Def.

Physical Mirror (lvl 1) - A shield power that reflects back buffs/de-buffs one receives from physical skill attacks. Available when one is equipped with a shield.

Reflect Damage (lvl 3) - Temporarily reflects damage back upon the enemy excluding damage from skill or remote attack.

Shackle (lvl 10) - Provokes an enemy to attack and then temporarily puts them into a held state. The target cannot be affected by any additional hold attacks while the effect lasts.

Shield Fortress (lvl 6) - Increases personal shield defense rate. Continuously consumes MP.

Shield Slam (lvl 1) - A shield attack that interrupts an enemy's physical skill attack and disarms them. Available when one is equipped with a shield.

Shield Stun (lvl 52) - A brutal shield bash that stuns the enemy. The target can not be stunned or dazed again while this is in effect. Requires a shield.

Summon Dark Panther (lvl 7) - Summons a Dark Panther, 30% xp cost, crystals consumed.

Touch of Death (lvl 1)- Casts a curse of dark magic to the enemy while sacrificing one's HP. Cancels all the buff magic of the enemy. Significantly decreases maximum CP for a brief time period. Decreases resistance to debuff attack, and the effect of HP regeneration magic. Can be used while one's HP is 75% or below.

Ultimate Defense (lvl 2) - Instantly increases P. Def. and M. Def. significantly. User must remain still while it takes effect.

Vengeance - Instantly increases P. Def, M.Def and provokes nearby enemies' desire to attack. Transfers the target's status to oneself. Becomes immobile while skill is in effect. Available while one is equipped with a shield.

Passive

Armor Mastery (lvl 5) - Increases P.def for heavy / P.def and Evasion for light armor. 

Final Fortress (lvl 11) - Automatically increases P. Def. when HP level falls.

Focus Mind (lvl 6) - Increases one's MP Recovery Speed.

Health (lvl 1) - Increases resistance to Poison and Bleed.

Heavy Armor Mastery (lvl 52) - Increases P.def. with Heavy Armor.

Knighthood (lvl 1) - Increases P. Def. when wearing heavy armor. Shield Defense is increased.

Magic Resistance (lvl 51) - Increases M. Def.

Shield Mastery (lvl 4) - Shield defense rate increases.

Shield of Revenge (lvl 1) - Temporarily reflects damage from melee attack skills back to the enemy.

Sword Blunt Mastery (lvl 45) - Increases P. Atk. for Swords and Blunts.

Weapon Mastery (lvl 3) - Attack power increases.

Wisdom (lvl 1) - Increases resistance to Hold, Sleep, and Mental attacks.


Gracia Skills:

Iron Shield (lvl - 1) - Increases Shield Defense power with a certain chance when attacked.

Shield of Faith (lvl - 1) - Shield of Faith that protects party members. Maximizes P. Def. and M. Def. for affected party members and absorbs most of the damage they will receive while active.

Symbol of Defense (lvl – 1) - Generates a symbol that maximizes the defense abilities of those nearby. Applies to all targets within the affected area. The effect disappears if you leave the area. Level 2 or higher Battle Force required. Consumes 1 Battle Symbol.

Level Up areas:

Well this is like i lvl up Dark avenger in most of my played servers.

1-15 lvl - Talking Island
15-25 Lvl - Ruins of Despair 
26-45 lvl - Cruma Marshlands
46-65 lvl - Dragon Valley
66-75 lvl - Swamp of Screams
76-80 lvl - Imperial Tomb

Dark Avenger aka Hell Knight