'You are fortunate. The creature which you faced could not have been a true Onod. You could not possible have faced the might of one the Old Ones.
'Nor would you have to, for the Onodrim are friendly to the Free Peoples on the rare occasion their paths meet. The great forests are less-travelled now than they were in days past, and few now ever see one of the great tree-herds.
'A small company of Elves from Mirkwood came to Imladris to consult with my father. Perhaps one of them will know what manner of creature you faced. Speak with my father to arrange an audience.'
Elladan is greatly concerned about the evil that seems to grow from deep within the Trollshaws and knows that you cannot face it alone.
Talk to Elrond
Master Elrond is at Imladris, far east of the Elladan's camp of Thorenhad and above the Bruinen.
Elladan has asked that you speak with his farther about arranging an audience with the visiting Elves from Mirkwood, who might have some experience with creatures of the manner which you encountered.
Talk to Legolas
Legolas is at the Haven of Orladion, just outside the House of Elrond.
Master Elrond has asked you of the Elf-prince named Legolas, currently staying in Imladris for a time. He hails from Mirkwood and may have some knowledge of the creature you faced in the Trollshaws.