9. Murai - Ninja Gaiden
While Yakuza 0 is a relatively easy game outside of a few tricky boss fights, Ninja Gaiden is an absolute, infuriating ass-kicker from start to finish, and is generally accepted to be one of the most difficult video games of the last 20 years.
And Team Ninja enthusiastically threw players in at the deep end with the game's first boss fight against rogue ninja Murai.
This is a boss fight so challenging many players never actually got past it, and only through perseverance and intense determination could anyone continue on.
Murai is a dab hand with nunchucks and will absolutely punish you if you let him. Dodging is absolutely vital to avoid his debilitating attacks, but even then, you'll need to find those brief windows of vulnerability to start chipping away at his health.
Though the fight is certainly effective in teaching players that they need to put in the graft to expose an enemy's vulnerabilities, that doesn't really make it any less annoying when you've been felled for the 15th time in a row.