Mark of Darkness
You succeeded in defeating the Master of Splendor Anays at Priest Greymore's request. But you received the Mark of Darkness rather than the Mark of Splendor. If you take this to Greymore, he will laugh at you.
Not dropped by monsters.
Cannot be spoiled.
The chances are official (x1). On servers with x10, x100 and higher rates, drop and spoil come more often.