Zakum's Arms
Zakum has eight arms that are named sequentially. Four arms exist on each side of the boss and you must defeat these arms before you can attack the base creature. Each arm has specific traits. For example, Arms 1 and 2 deal magic attacks that drain your magic while Arm 3 emits a poison mist that blocks your skills. Other arms do physical damage and even heal the monster. As you defeat the arms, Zakum should become easier to defeat -- especially after defeating its healing arm.
Accuracy
Accuracy is a statistic that determines how likely you are to hit a monster. Because Zakum has so many defenses, some of your attacks may miss. This is one of the reasons the party quest can take so long. A monster with lower defenses is susceptible to more of your hits. At level 130, you need slightly higher than 50 percent accuracy to hit a monster at or below your level. To damage one of Zakum's arms, you need accuracy of just under 73 percent. Required accuracy declines, little by little, the closer you become to 140.
Increasing Accuracy
You may be able to increase accuracy above your base percent by using armor and weapons that increase accuracy. For example, level 125 Moonsteed boots for thieves offer additional accuracy of 60. You can also improve upon your current armor by using scrolls to change stats. For example, the "Scroll for Claw for ATK 10%" will increase your accuracy by three percent when it succeeds while the "GM Scroll for Claw for ATK 100%" adds 40 to your accuracy.
Considerations
Because Zakum is level 140, most guides recommend that you wait until level 130 before embarking on the party quest. You may wish to wait until you are level 140 to further increase your accuracy and defenses and be able to use more protective equipment. If you're a dagger thief, which must be close to the monster to attack, have many health potions on hand and wear armor that increases your defenses against magic and physical attacks. Assassins, with their ranged attacks, are not as close to the fray but health potions are still important.