ToME: the Tales of Maj'Eyal

I've recently started to play this nice game, and with my lvl 20 thaumaturgist, tried the wight grave quest.
I destroyed the first wights with ease, but once I met the Barrow-king, it killed me in one hit with a 200 damage nether ball (I had 150 max hp).

That was a sudden death, and I'm now wondering where did I go wrong:
- Was it just bad luck ?
- Should I've waited to gain more levels/hp before doing this quest ?
- Is it advised to find nether resistance before fighting the barrow king ?

Also, I understood that the old website/wiki is down, is there other places where I can find beginner-friendly information about the game ?

Thanks for your future help, gentlemen.

Level 20 is definitely quite early. (It doesn't help that the level/danger ratings of the quests is sometimes wildly off. Can't remember what the BW quest says.)

You might be able to get away with if you have rNether and enough speed, but it's going to be a bit risky unless you're quite a bit higher level.

150 hp isn't enough for any of the quests other than the Thieves and Wolves ones. Maybe a speeded-up sorceror could one-hit the king with Fireflash and get away with it, but I wouldn't advise it.

You might want to try an easier character if you are starting out. A zombie RohanKnight Swordmaster, for example. Max out swordmastery, weaponmastery, combat, and then antimagic.

Troll sorcerors are relatively forgiving if you want to play a magic user.