Hi. I rarely post on forum’s. im trying to be a self learner also when it comes to GD. im kinda new to the game mainly because i play only HC mode that comes with R.I.P’s but i did put lots of hours into it till now and i think i did learn alot . to this point when i died i did know what i did wrong but this thing … idk
i did use this build
pretty much rushing rushing through normal weteran mode. i was lvl 59 in the moment i think halfway malmouth story facetanking everything on the way with no problem. 10k hp i guess and caped ress with nice armor . suddenly i did hear strange demonic voice and my hp bar was just gone and rip. there were no boss , no nemesis since i did not unlock them yet. just this voice and insta death. what was that 
?
What’s the name of the area you were?
somewhere close to tomb of herald Mathis since it was just after i left the tomb and walk a bit more
You might have run into Fleshweaver Haraxis, who is a boss and spawns in the area after the tomb. I find him easy to miss among other mobs. He is also deadly, but I find it strange that you were killed so quickly.
thanks for answer 
well im sure that i was not low on hp. did felt confident since i could basically stand for a minute tanking other bosses but i always keep and eye on hp bar and that this just melted in frame also with 70% aether ress.
Haraxis can debuff your resistances pretty hard
ohh i see . i might just went into his combo droping my ress in huge amount and didn’t notice cause it bursted me so fast. well new lesson learned
Yeah he can also spawn on malmouth harbor. I always aware of him cause he is as tall as other yellow brothers. I died in Sc too by him. I always notice him when my Hp bar suddenly go down i know it is him so i run back and prepare for hard fight. U have 33% chane to not avoid him cause one of tthe spawn is a narrow route where u have to go.
If u go for the dock quest, then he is there in an dead end too. U can skip him but u have too sneak a bit to avoid him.
well im starting all over and now i will be prepared that’s what i love about hc. You randomly walk whistling and Your dead and that going into end game and discovering new game content is more rewarding thanks for answers guys… damn i really didn’t expect so strong guy in that kind of random place tho
Never, ever underestimate what our sneaky devs are likely to have waiting for you just around the corner.
Mobs that can kill me even i did 50 chars and builds too:
Kilrian (Optional): He is not that big guy but his aether spear has vita dot and u don’t have much in the early game. So it can be though he hits u with that.
Guardian of Solael (Optional): He is chaos pool is insane so U have to dance with him. Even he can lifeleech.
Lucius: Ah yes. He is one of the hardest. Most of his attacks hit like a truck. Luckly most of them can be avoid.
Bollag, Keeper of the Gates: He can be deadly with his ball, but still can be avoid. U can stay on the stairs and shoot him sometimes he stucks.
Theodin Marcell: Can be pain too. I don’t go him. I always go to elite, if i unluck the faction. So don’t know how dangerous now.
Sentinel (Optinal): He can be pain too. Melee harder.
Father Kymo: His jump attacks reduce ur Da. So u can start that fight with lower Da, than all his attacks hit like a truck.
Korvaak (Optional): Can be deadly in all his forms. 
That’s all that i remember had hard fight or need to be more cautious.
@cubix199 ,sorry that your Opressor died.
Other than Nandi suggestions,there few other dangerous bosses.
Like Ekket Zul,his fissure attack was unpleasant surprise the first time I met him.
The witch from Barrowholm quest.She can shotgun one shot you.
Shar Zul,fire tornado debuffs your resistances a lot.
Salazar,don’t stand in the pentagram.
Of course I will leave you discovering other bosses mechanic.And ofc be aware of ground damage.