Great black mass is DEAD, R.I.P.
The magic mist around the dead Great black mass's neck leaps to your Kerbholz.
A new mark appears.
Congratulations! You have just completed Legendary monsters!

CONGRATULATIONS, YOU HAVE COMPLETED THE LEGENDARY MONSTERS QUEST!

As a reward, your kerbholz's ring is now coloured according to the level of
the target.
You have joined the elite few of this mud, mortal, and for that, you have a
new quest visible in your completed quests, and alongside that, you have a new
rank 'Vanquisher'

All monsters and fiends through heaven and hell stand in awe and revere Andthi
as she proves her worth by vanquishing all that stands in her path.

... Took nearly 10 years to finish the freaking quest. Talk about commitment
towards a video game!