Samurai Revised

I took the official Samurai class and remade it, tweaking some features  and completely changing others. The changes may be unbalanced as this is my first homebrew, so feedback is appreciated.

Bonus Proficiency

When you choose this archetype at 3rd level, you gain proficiency in one of the following skills of your choice: History, Insight, Performance, or Persuasion. Alternatively, you learn one language of your choice.

Fighting Spirit

Starting at 3rd level, your intensity in battle can help you strike true. As a bonus action on your turn, you can give yourself advantage on your next weapon attack roll.

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Elegant Courtier

Starting at 7th level, your discipline and attention to detail allow you to excel in social situations. Whenever you make a Charisma (Persuasion) check, you gain a bonus to the check equal to your Wisdom modifier.

Your self-control also causes you to gain proficiency in Wisdom saving throws. If you already have this proficiency, you instead gain proficiency in Intelligence or Charisma saving throws (your choice).

Mindful Slash

Starting at 10th level instead of attacking multiple times you can concentrate on one deadly blow. When taking the Attack action,  you can give up any number of Extra Attacks to add the damage dice of your weapon a number of times equal to the extra attacks you are giving up. Your critical range amplifies by 1 up to 18 for every Extra Attack you give up until you hit with an attack on this turn or the start of your next turn.

Mortal Unsheathing

Starting at 15th level, when you score a critical hit on an attack, you can use your reaction to immediately make a second weapon attack against the same target.

Strength before Death

Starting at 18th level, your fighting spirit can delay the grasp of death. If you take damage that reduces you to 0 hit points and doesn't kill you outright, you can delay falling unconscious and immediately take an extra turn, interrupting the current turn. While you have 0 hit points during that extra turn, taking damage causes death saving throw failures as normal, and three death saving throw failures can still kill you. When the extra turn ends, you fall unconscious if you still have 0 hit points.

Once you use this feature, you can't use it again until you finish a long rest.