What are the most dangerous bosses (one hot mechanics)

Playing on HC and im little bit nervous going to the Mighty Silverfist fight..

Also Zalmarath the Colossus killed my softcore char multiple times per one shot even if i have like cap res, and 50% phys reduction.

Are there others like these two (one shots) in the campaign?

Colossus seems to be bugged with that attack. Does mysteriously way more damage than all of his other, more telgraphed moves.

Silverback will one shot you yes, what I would do is practice him on SC a bunch of times before you fight him. Do not fight until you're sure you can do it without dying.

Same for Blackjaw. If you really value your HC character, practice them multiple times on SC until you're sure you know all of the one-shot telegraphs.

Viper Naputzi was damn annoying, mostly due to that final shield attack stage.

Silverfist - Long range one-shot with little telegraph and low cooldown.

Executioner - Anvil drop one-shots but it's the only thing you have to worry about this boss.

Mortar-throwing miners in Mawdun Quarry basement - Not a boss but their mortars have low visibility and can shotgun.

First Boss in Ultimatum Stage 4 - Birdy. As soon as he wraps his wings around his body you got like two seconds, otherwise the whirlwind will kill you. Not one shot by definition but death sentence.