king thranduilKing Thranduil is described as having lived in the original elvenElven city with his father which would make his birth in the first age. In that light it seems likely that dragons would have been more abundant and in sheer speculation I would imagine that the elves would have done battle with them at one point or another. Since thranduilThranduil is a son of kings it would be more than a good chance he would have been some brand of warrior and present during any significant conflict. ThranduilsThranduil scare reappearing may simply be that since dragon fire is magic it cannot be fully healed and therefore he conceals it with some sort of glamour charm. Most people seem to have this questioning as to how thranduilThranduil would have such a power but if he's as old as the scriptures suggest " first age" it seems likely that he may have developed unusual abilities not common to lesser elves. Galadriel for instance can somehow magically appear out of thin air, and elrondElrond seemingly has the ability to see the future so I can only surmise that thranduilThranduil being every bit as ancient as any elf in existence had developed some illusion based magical abilities which would seem fitting since murkwoodMirkwood can disorient the mind.