That was the quest with Gauldur's (Gauldar?) Amulet, wasn't it? Yeah, that was a fun fight. But my character was powerful enough then for the battle to be challenging but by no means impossible.

Forbidden Legend is a nasty quest for that one battle...

3 doppleganders every 30~45 seconds all capable of using unrelenting force, thankfully they all have like 1 HP and there are 2 pillars you can hide behind, the rest of it is easy in my opinion. Just use unrelenting force first to try and dispel a couple and arrows/destruction spells on those that remain... That boss is pants without his doppleganders.

I won't spoil the quest where this battle took place but I had to face a Drauger Deathlord at level 19-20ish. Definitely the hardest battle that I fought so far in the game. It was made even harder by the fact that the (Censored) kept disarming my weapon. I had an Ebony Sword that I got from the 1st Deathlord I fought (Just as tough but for some weird reason it was a much easier fight) but then the 2nd one I fought disarms me and I can't find the weapon and he keeps knocking half my health off with every hit of his Honed Ancient Greatsword(Thank God it wasn't ebony). To make matters worse I'm roleplaying where I'm not wearing a Helmet, I'm only wearing Light Armor, had already used Warcry earlier (It failed against the 1st deathlord) and I'm now down to the Dwarven Sword that I had when I entered the dungeon and even that weapon gets disarmed. I finally got him 10-15 minutes later of backtracking, Fast Healing, attacking him with the Dwarven Longsword. Thankfully my Ebony sword was right on the stairs but in a place where I wouldn't have found it in a timely manner, well before the deathlord would kill me. Ancient Dragons, Alduin, Dragon Priests, Bandit Chiefs, Briarhearts, none of those enemies gave me the fight that I had with that one Deathlord, unreal.

well ancient dragons does not appear in the game before you hit the lvl 30 mark, so thats no true. Krosis and the "normal" dragon you meet are a hard fight anyway att low lvl

I kinda have two,

In side I would say Vokon,
Outside I would say the big Forswarn camp near Morthal,

both vs my level 18 Magi