Samurai Shodown .... the whole game series....
Almost every Boss (except Amakusa in SS1) is an all-countering prophet of virtual fighting mastery or is extremly agressive to the point of impossibility till you randomly beat them (Happens often btw) .
Zankuro Mizakuchi is my blood-pressure death .
Trying to beat this guy is like kicking the wall down , only using with my pinky toe .
The thing with Samsho is that the bosses can range from either "Eh this is stupid but okay" to "FUCK THIS FRANCHISE".
Amakusa (SS1): This guy is an asshole. Reads you every single time, you can't land a hit on him. Last time I beat him (PS1 version), I just threw him over and over like it was SFV on ranked.
Mizuki (SS2): My favorite boss fight, but that doesn't exactly make it good. I like it because it's the stupidest boss with the stupidest attacks I've ever seen. A projectile that inverts your controls, AND a super THAT COMES BACK BEHIND YOU IF YOU JUMP IT? That's the craziest thing I've ever seen, lol.
Zankuro (SS3): There's lots of things wrong with this battle honestly, and most of them are because of the game itself. It feels so sluggish to play, no matter the version. Not to mention, you have to beat him 3 times, and he can kill you with three swipes.
Amakusa/Zankuro (SSIV): My favorite Samsho game, and the bosses are okay. Not the best but not the worst. Amakusa might be hard but only because he has massive range and plays defensively 90% of the time. Zankuro hits like a goddamn truck in SSIV, vanishing a lifebar in a single hit sometimes. Potential hot take, but they might be the most "fair" bosses in the franchise.
Gaoh (SSV, specifically Vanilla SSV): FUCK THIS GUY, SO MUCH, LOL. He pulls a Rugal where the problems lie if you beat him one round, where whenever he gets full meter, he becomes a armored demon monster and becomes INVULNERABLE TO EVERYTHING, and keeps spamming a dashing attack where if he hits you, it's not only a weapon drop, but massive damage. And it might happen over and over in a single round, so you have no choice but to keep running away.
Makai Gaoh (SSVI): This guy can also eat a bag of dicks, lol. Massive range, the most damaging command grab I think I've ever seen, and a Final Psycho Crusher knockoff super. Also blocks everything and decimates you if you even blink wrong. Sure, busted boss for a busted game, but Makai Gaoh is pretty annoying to fight. At least he doesn't have an invulnerable state, I guess?