Name: Master Assassin
Difficulty: 20
Base level: 15
Base experience: 500
Speed: 12
Base AC: 0
Base MR: 30
Alignment: 18
Frequency: unique, no random generation
Genocidable: No
    Projectile as weapon, or if in range, uses melee weapon for 2d6
    Projectile as weapon, or if in range, uses melee weapon for 2d8
    Steals the amulet etc.
Weight: 1450
Nutritional value: 400
Size: medium
Resistances: None
Resistances conveyed by eating: None

Master Assassin is humanoid. It is an omnivore.

He strolled down the stairs, followed by a number of assassins. When he was directly in front of Ymor he said: "I've come for the tourist." ...

"One step more and you'll leave here with fewer eyeballs than you came with," said the thiefmaster. "So sit down and have a drink, Zlorf, and let's talk about this sensibly. I thought we had an agreement. You don't rob-- I don't kill. Not for payment, that is," he added after a pause. Zlorf took the proffered beer.

"So?" he said. "I'll kill him. Then you rob him. Is he that funny looking one over there?"

Zlorf stared at Twoflower, who grinned at him. He shrugged. He seldom wasted time wondering why people wanted other people dead. It was just a living.
"Who is your client, may I ask?" said Ymor.

Zlorf held up a hand. "Please!" he protested. "Professional etiquette."
The Colour of Magic, by Terry Pratchett