Maybe It's Grendel!

Requirements

Inside Grendel's House - Click to enlarge

Hersha will tell you to raid Grendel's Magic Library.
Head to the middle of Ellinia where Grendel resides.
Enter Grendel's House.
When you enter the portal, it will be empty, and you'll have 10 minutes to search.
Click on the pile of books on the shelf on the left (highlighted in red and black in the image) and a figure will walk out, giggle, and disappear.
A large number of Dangerous Blue Mushrooms will spawn along the floor and the portal will not allow you to exit until you defeat all of the Dangerous Blue Mushrooms.
Once you have defeated the mushrooms, you will be allowed to leave and return to Hersha.

It is recommended you bring a large supply of HP and/or MP potions with you to battle the large mob of mushrooms with.
If upon attempting to enter Grendel's house you are told that Grendel is still inside, try changing channels or waiting until the player inside leaves.
It is also recommended that you stand on the shelf highlighted in green and black in the image when you click on the books to avoid being immediately run over by the mushrooms.
The box and the barrels on top highlighted in blue and black in the image make excellent sniping spots for ranged classes who are unable to do battle at short range. However, once attacked, the mushrooms will sometimes jump up to get you - so be careful all the same!
Should you die while battling the mushrooms you will only lose 1% of your experience as this is a "protected" map.
Should you run out of time, die, or disconnect from the game, you will be returned to Ellinia and the quest will be counted as completed (if you clicked on the books and summoned the mushrooms). This can be used to escape without killing the mushrooms if you are unable to.
Activates quest: Done with Ellinia