Soul of Cinder? One-shot.
Dancer of the Boreal Valley? One-shot.
Nameless King? Three-shot.
Iudex Gundyr, the "tutorial boss"? Still kills me 5-10 times whenever I make a new character, because I effectively "forget" how the game works.
I maintain that Gundyr is a piece of filth and completely inappropriate as a tutorial. As far as I can tell, his main purpose is to inflate the ego of veteran players.
For anyone who struggles and doesn't want to waste hours of their life on him, just make a sorcerer or pyromancer and then follow whatever path you want from there.