I'm in Under Saarthal, and the Dealthlord's kicking my butt! I'm lvl 20 battle mage/thief. mostly destruct/conjuration spells. Any advice?

Attack when you have a distance, sprint away when he gets close, if your level 20.. then I'm sure he can kill you in two-four hits!

I been beating some tough oponents with Potion/draught/elixir of Health at Lvl 15 to 20. This gives you more health for 1 minute or so. You might also want take a potions that increase your mana as well. In my playthrough as a mage, I found that the lack of mana was what was preventing me from using enough higher level spells that do more damage to take out tough opponents.

Run in loops up and down teh stairs to keep away from him while dorpping Fire runes for him to hit chasing you.

On the off chance you mean teh final named boss, he seems to change his resistances up alot somehow, so you have to vary elements mid-fight.

My first encounter with that death lord? He shouted me against the back wall. "DA!!!" What a comeuppance.

I stopped having too much trouble with them around that level, but I'm playing a basher (well, slasher, but a melee nonetheless ). If you have the Amulet of Talos it will reduce the Shout cooldown by 20% and if you have the Unrelenting Force Shout fully 'worded' it acts as an interrupt and a stun, plus if they are near a wall behind them it will do damage when they slam against it. I usu Shout them against the wall and wail on them before they can get back up - you might be able to tailor your fighting style around that Shout. :\ Otherwise, kite and potions maybe?

Another option could be to look up where all 3 words are for the Time Slow Shout and use that?

Edit: Now that I've suggested that I'm betting that the Time Slow Shouts are in dungeons guarded by Deathlords.

What spells do you have? Scrolls? I found J'Gargo's experimental scrolls susprisingly useful against them, although you need to watch your health.

If you're meaning Jyrik Gauldurson.... the boss slumped in the throne near the Eye of Magnus....

You have to wait until Tolfdir uses his spell on the Eye before you start whacking on Jyrik - and keep firmly in mind that ONLY melee attacks work on him.. And he's the EASY one of the Gauldursons....

i destroyed him with 20 seconds of flame

Ah, crap - my game is literally saved right after killing him.

Indeed, he varies his resistances (you can tell by his color of shield around his body), but if you are lucky, he gets frost and shock first, so you kill him with flames

At low level, it sometimes helps If you can get the Deathlord to chase you into an oil slick, or onto a ledge (which might be several rooms away).

They don't seem to like fire or falling damage.

Can't recall whether that applies to your particular situation.

I started a new char last night (Khajiit whom I want to be battlemage, my first ever magic char) and he's just a wanderer avoiding main/guild quests for now until I figure out how to actually use a mage character. So I stumbled across the moonstone mine where they accidentally dug into a nord burial site on ~lvl 6 playing expert with a random follower that I brawled with in the silver-blood inn.. Did alright against the regular draugrs, although the follower guy just kept standing in front of me getting crispified by my flames and he eventually died. So then I saved after he died because expert mode is pretty damn challenging for me I've been saving every 5 mins and accidentally overwrited the save where the follower was still alive.. And proceeded to get my ass handed to me by a deathlord for about 2 hours.

The way I finally killed him was to eventually run like crazy in the room, dodging fireballs from a stone pillar, raid the chest next to his throne and found a fire enchanted sword, then ran back out (He wouldn't enter the tunnel I was in, nor would he stand at the entrance long enough to be killed) and waited for mag/HP/stam to recharge fully. sneak attacked him with a poisoned arrow (weak aversion to fire, that I'd found somewhere on my walk beforehand) then equipped flames and the firey sword and wailed on him where I was *just* protected from the stupid pillars fireballs. I was juuust about to die again when he took a knee and I got a lvl up, so did that to recharge all my stats and then finished him off.

I realised the gameplay difficulty was on apprentice the other day and decided to up the ante because apprentice was pretty easy, didn't think expert would be this hard, although it could also be my complete ignorance about how to play a mage char. Not sure if that will help you any at lvl 20 but at least you're not the only one getting owned by deathlords lately.

Something apart from fire that I find very useful on these guys (and others) is to use a paralytic enchantment on your melee weapon. Nice to have them topple over and then you can just hack away until they recover enough to be paralyzed again. You could use a paralyzing poison on your bow, too, but I know most draugr resist poisons.

i'm still wondering what deathlord is so dificult there. i mean the under saarthal quest. with a stealthy archer i did it without problems.
the difficult part was the gauldur quest which pittet mme against the 3 sons. that was a real problem. really made me run for my life a lot of times. there i lost lydia to the first one, and had to manage somehow.
dificulty expert