The official GemStone IV encyclopedia.
Rumors speak of the dark assassin being a vague being that is sent to quiet those who tell secrets best left unheard and to punish those who fail to abide by their oaths. However, many are quick to dismiss these rumors as false tales and unnecessary paranoia. After all, there are few who can claim to have seen one of these vague beings... and fewer still who are alive to tell about it.
One generally cannot see a Dark Assassin as though it was a normal critter in the room. Dark assassins are GameMasters (GMs), and kill by instantaneous GM-based messaging.
Dark assassins that are visible are named GM-played NPCs, the most well known one being Lacheis. He kills his target by throwing daggers that cannot miss.
At one point characters could be killed by an NPC monster labeled "Dark Assassin," but this method has not been seen in quite some time.
Example text: The script type dark assassin
You hear a chilling voice whisper in your ear, "Continue to test our patience, and we will certainly see our commitment to silencing your flapping tongue."
Some time passes...
Your head snaps back suddenly as a hand clamps over your mouth and pulls you backwards. Three slashes across your throat cut short any attempt to scream.
... 175 points of damage!
Incredible slash to your neck!
Throat and vocal cords destroyed!
Zero chance of survival.
The air about you stops shimmering.
The buzz of thoughts in your mind subsides.
The bright luminescence fades from around you.
The silvery luminescence fades from around you.
You no longer feel so dextrous.
It seems you have died, my friend. Although you cannot do anything, you are keenly aware of what is going on around you...
You mentally give a sigh of relief as you remember that the Goddess Lorminstra owes you a favor.
...departing in 14 mins...
You struggle briefly, but you collapse and fall to the ground as your strength fails. You barely make out the shadowy figure looming above you as your vision blurs and your senses grow dim. You can still hear the words cold and clear before everything goes dark,
"That is a high price to learn the value of silence."
Everything goes dark and the last thing you hear are faint footsteps and a sinister laughter fading away.
And the NPC type Dark Assassin:
A dark assassin screams loudly, its shrill cry expanding outward with waves of magic!
CS: +535 - TD: +4 + CvA: +18 + d100: +30 == +579
Dragonlance screams in agony and falls to the ground, grasping his head with his hands!
The assassin stops screaming to attack Dragonlance!
A dark assassin claws at Dragonlance!
AS: +360 vs DS: -117 with AvD: +36 + d100 roll: +2 = +515
... and hits for 153 points of damage!
Massive blow smashes through ribs and drives Dragonlance's heart out the back.
- Dragonlance drops dead at your feet!
Dragonlance is able to move again.
A dark assassin cries, "Another meal for my empty soul!"