On the topic of Soulslike games - Genichiro/Sword Saint Isshin from Sekiro: Shadows Die Twice is probably my recent favourite.
You start the game and face off against the unbeatable boss Genichiro. Wrecks your shit with unblockables that you don't know how to avoid and fast combos and cuts your arm off. Then at about the 1/3rd mark of the game, you fight him again where he is this skill gate boss that you have to break through. You spend ages figuring this dickhead out, from his parry combos to unblockables, to when to heal because he pulls his bow out every time you do it. You beat him, and he demonstrates the "lightning return" ability that becomes invaluable later. Beat him, but he escapes.
He then shows up as the final boss, and is a complete joke at this point. He then kills himself to bring back his grandfather in his peak form, the Sword Saint Isshin. Throughout the game you are told how much of a badass this old man is, except he's sick, and he lives up to it completely. He does flying slashes, guard breakers, unblockable 360 degree slashes and so on. You knock off his first health bar, and he pulls out the spear of the guy he killed in the very beginning intro cutscene, completely changing his moveset, including using a rapid fire pistol, in addition to all the flying slash shit from before. Then the weather turns, and he starts using lightning attacks, prompting you to use the lightning reversal against him like you did with Genichiro's first fight. Fight ends with you splitting open his guts, him still standing and accepting the outcome, then asking you to seppuku him by beheading him. The pay off? After that you can use his flying slash attack in NG+. It's also all set in the place where you lost your arm at the beginning of the game, in a Ghermin styled flowered area.
Great final boss. Very enjoyable and a good test of skill.