Unseen and Unseeable

Unseen and Unseeable is a kill quest given by Argent. Part of its requirements require killing a boss mob.

How To Achieve
At low levels, Rikis can be very dangerous as they have high attack speed and damage, also with the fact that they can be almost fully invisible, except for their floating daggers.

As for the boss, Rikimaru's presence is only dictated through a boss health bar and its sounds. There is no way to find out where Rikimaru himself is, except setting him on fire or throwing a Splash Potion at him. Be sure to use Flint and Steel or Fire Aspect enchanted weapons or Bows with Flame enchantments to keep his location visible.

Both kinds of mobs have low health and defense, hence their reliance on stealth, so they should be easy to kill if focused down. Remember, you have to deal the killing blows to each of the mobs, not other mobs, other players, or environmental damage.

Once all requirements are fulfilled, return to Argent and talk with her to finish the quest.