Blitz Knight

A knight drenched in the blood of countless combatants stands on a mound of his victims. As another hoard of demons approaches, he lets out a hearty cackle and readies his blade once more. An old Half Orc woman unleashes a brutal combination of punches and kicks during a martial arts tournament. Every blow building from the last, the final hit is a brutal uppercut that sends her human opponent out the ring. She grimaces as she turns towards her next opponent, cracks her knuckles and gets ready for the next match. A young man, clad entirely in black, hides in the rafters of a building, spying on the individuals below. They all seem preoccupied with their lavish meal. Before the dessert course is served, an onslaught of arrows hails from above. Every arrow embedded in the necks of their foes deeper than the last. This is the way of the Blitz Knight. Relentless, persistent and brutal. Blitz Knights are at home on any field of combat. An old saying from their homeland is as follows: “The Blitz Knight a drummer Of an endless Percussive dance If you hear their crescendo, You never stood a chance”

Credit belongs to Offbeat Outlaw for this subclass, i just transported it to dnd beyond

Blitz Stance

Starting at 3rd level you gain access to a style of fighting that grows stronger with consecutive strikes. As a bonus action you may enter into the Blitz stance. Until the start of your next turn, every attack hit in a row without missing increases consecutively in damage by 1d4. The first hit will have 1d4, the second will have 2d4, the third 3d4 etc. every consecutive hit gaining momentum and ferocity. Upon missing, the combo is reset back to 1d4. If you take damage in the middle of your turn, you must make a concentration saving throw in order to maintain the combination. If you fail, the combo is reset back to 1d4. Combos are always reset at the end of a turn. In the case where attack rolls are rolled all at once, roll them sequentially instead. Blitz Stance is so physically taxing that the user must forgo defense and cannot benefit from the use of a shield until the start of their next turn. You may enter Blitz stance a number of times equal to your proficiency bonus and recover uses on long rests.

Ferocious Gait

The training required to learn the ways of the Blitz Knight has shaped your body and your mind. At 3rd level, you may now use your Strength or Dexterity Modifier in place of your Charisma for intimidation checks. You also gain proficiency in the survival skill. If you already have proficiency, you may double your proficiency bonus for this skill

Overwhelming Presence

At 7th Level your prowess on the battlefield precedes you. When rolling initiative, you may choose a creature you can see to intimidate. Roll a contested check of Intimidation, yours versus theirs. If the opposing creature loses, they must roll initiative at disadvantage.

Adrenaline Rush

Your thirst for bloodshed extends to your resolve. At 10th level, after using Blitz Stance, you can use your reaction to gain temporary hit points equal to the number of consecutive attacks hit multiplied by half your fighter level. You can use this feature immediately after a miss, a loss of concentration on your combo, or if you finish your combo. This feature will count the hits of the most recently landed combo. You may use this feature once and then must be recovered on a long rest. The temporary hit points gained from this feature disappear 10 minutes after combat ends.

Persistent Swing

At 15th level you learn how to cover for your own mistakes. Upon missing an attack, you may recover quickly and attack again. Using your reaction, make a weapon attack against the target you missed, on hit roll damage without adding your damage modifier. This hit cannot benefit from any extra damage accumulated by Blitz Stance. Hitting with this weapon attack roll will negate the miss and allow the combo to continue.

Flaming River

At 18th level you become a torrent of battlefield destruction. If you reduce an enemy to 0 hp while in Blitz Stance, you may use another use of Blitz Stance in order to give yourself another action. If you kill an enemy on a reaction while blitz stance is active, you may invoke this feature to immediately interrupt the current turn and take your action.