Battles of the late Third Age

[Nilpaurion Felagund]

take random slimy Hobbit-creature back to the dungeon

Just a correction: Gollum was not imprisoned in a dungeon.

...and we had not the heart to keep him ever in the dungeons under the earth...

OK, back to topic. About the assault; Thranduil's kingdom is not far from the eastern eaves of Mirkwood, right? Maybe the assault came from the east...unlikely?

Yours, if you want to
->The True Son of Finrod, and of Amarië the Vanyar