Samurai, Variant

Iai Warrior

For the archetypal samurai, a battle is as much an art form as it is a test of strength. The Samurai seek out challenging fights and uphold a great sense on honor in combat. A fighter who takes on the samurai subclass becomes adept at the ways of wielding two-handed weaponry.

Stances

When you choose this subclass at 3rd level, you learn special stances to increase your effectiveness in combat. You learn two stances when you gain this feature and one more of your choice at 7th, 10th, 15th, and 18th level. You can use a bonus action on your turn to enter a stance if you are wielding a melee two-handed weapon. The stance lasts for 1 minute until you change stance or until you are knocked unconscious.

Earth Stance

While you are in this stance, you have advantage on Strength checks made to grapple and can hold a two-handed weapon in one hand whilst grappling a creature. Additionally, on one attack per turn, you may use your bonus action to gain a bonus to your AC equal to your proficiency modifier if the attack hit. This bonus AC lasts until the start of your next turn. Also while in this stance, your feet are planted firmly on the ground, doing this grants advantage on Strength saving throws and disadvantage on Dexterity saving throws.

Fire Stance

While in this stance, you focus all you have on offence by sacrificing your defenses. The first attack you make each turn is made with advantage. Additionally, you suffer a -4 to AC as long as you are in this stance. When you hit a creature with an attack, you may add your Proficiency Modifier to the damage roll as fire damage, which also doubles on a critical hit.

Lightning Stance

As long as you are in this stance; if you use the Dash action, you can attack all the enemies that you come within weapon range of. These attacks require your bonus action. Treat them as critical if they hit enemies who are unaware of you and are unprepared for the attack. Also, you can use your action to attack a single target furiously 3 times. These attacks are incredibly fast but difficult to land accurately, and as such attack rolls are made without proficiency or ability score bonuses (damage is dealt normally with each hit). At the 10th level, you can use this stance to attack a single target 5 additional times without proficiency bonus.

Stone Stance

When you enter this stance and at the start of each of your turns while you have at least 1 hit point or more remaining, you gain a number of temporary hit points equal to your Constitution Modifier (Minimum of 1) + your proficiency bonus. These temporary hit points stack, and will last until you are no longer in this stance. Once per turn, when you hit a creature with a weapon attack, you deal an additional 5 weapon damage to the creature. Opportunity attacks made against you are rolled with advantage and if you use more than half of your movement speed in a turn, this stance immediately ends.

Water Stance

When you successfully hit a creature with a melee weapon attack while in this stance, you may immediately spend your bonus action to attempt to knock the creature prone. If you do this, you force them to make a Dexterity saving throw equal to (8 + your Strength modifier + your proficiency bonus). Failing this attempt grants the creature advantage on their next attack roll made against you. Additionally, while in this stance, landing an attack of opportunity on an enemy reduces that creatures movement to 0ft until the beginning of its next turn.

Wind Stance

While in this stance, you become both quick and maneuverable. You may take the Dash or Disengage action as a bonus action, and you ignore difficult terrain when you Dash. Melee attack rolls made against you are at disadvantage, and upon an attack missing, you are able to make an attack of opportunity against them if they are within weapon range. 

Surge of Energy

Starting at 7th level, your intensity in battle can shield you and help you strike true. As a bonus action on your turn, you can give yourself advantage on all weapon attack rolls until the end of the current turn. When you do so, you also gain 5 temporary hit points. The number of hit points increases when you reach certain levels in this class, increasing to 10 at 10th level and 15 at 15th level. Your unarmed strikes count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

You can use this feature three times. You regain all expended uses of it when you finish a long rest.

Fighting Spirit

At 10th level, when you use Second Wind you gain resistance to piercing, bludgeoning and slashing damage from non-magical weapons until the start of your next turn.

Iai Strike

Starting at 15th level, you have learned to cut through anything. 3 times per long rest, whenever you use the Attack action, your melee weapon attacks have advantage until the end of your turn, and your weapon counts as magic for the purpose of overcoming resistances and immunities from non-magic weapons and damage.

Wrath of Iai

Beginning at 18th level, you can add 5d10 to a damage roll when you choose the Attack action on your turn. This can be done a number of times equal to your proficiency modifier doubled. These will be recharged after a short or long rest. You score a critical hit when you roll a 17 through 20.