Kalameet from Dark Souls was particularly nasty. Trying to tank his attacks is not a great ideas since his attacks will either break your poise or get close to, so you need to remain as mobile as possible. Unlike other bosses, he doesn't really have any clear openings when you can run up and swing at him so you just need to hit him whenever you can.
Death from Castlevania 1 without subweapons is also very difficult. His attacks are random and they hit hard, on top of this Death himself also moves around and he can trap you into a corner where he'll just kill you from contact damage. If that wasn't enough, the corridor before him is full of annoying enemies which you need to get past every time you want to try again.







