Dragon Knight

The knight's sword hisses from her scabbard, followed by an acrid tang on the wind; acid drips from the tip of the blade, pitting the bare stone at her feet. Two trolls circle her warily, while a third furtively climbs the cliff behind and below the outcropping. "A cunning ploy. For trolls," she thinks to herself with an inward smirk.

The two trolls howl and dash towards her as she raises her sword to meet them. The first troll sweeps at her legs, its claws whistling through empty air as a vertical leap carries her out of its reach. The second troll, attacking from above in anticipation, catches the warrior's arm in its slavering maw; both trolls howl with glee, another meal secured. "Almost," she admonishes, "but not quite." 

A sound like knucklebones hitting hard stone and another howl, this one of pain, echoes across the small outcropping as the knight's deceptively hard skin shatters the troll's teeth like glass. The third troll, believing itself to be unseen, lunges for her from over the cliff, the final part of the three-way attack. Blood sprays and the troll stares dumbly at the severed stump of its claw; in the blink of an eye the warrior had whipped her sword behind her back in a low sweeping parry, severing the limb without taking her eyes off of the two trolls in front of her.

Trollflesh sizzles and bubbles in the wake of her flashing sword, leaving all three trolls reeling; the knight lets out a low whistle and leaps from the cliff with a grin. The trolls, enraged, rush to the edge to watch their prey plummet to her death. A moment later, however, the knight rises back up astride a huge black dragonnel, longbow already knocked. The ensuing battle lasted mere seconds, leaving the world with three fewer trolls.

Dragon knights are versatile warriors, making excellent use of the famed resilience and preternatural senses of dragons. Dragon knights are equally quite skilled riders, able to take to any mount, but with special preference for dragonnel, wyverns, and other lesser dragons. Most dragon knights belong to one of the few small enclaves of dragon riders scattered across the land, learning esoteric and highly coveted lore from the mouths of ancient dragons.

Draconic Lore

By 3rd level your training in assorted draconic lore is more or less complete, granting you proficiency in animal handling, survival, and leatherworker's tools. Additionally, you learn Draconic. 

The skillset of the dragon knight is geared towards self-sufficiency; any dragon knight can, if needed, fashion a new saddle for their mount, survive in the wilderness, and communicate with others of their kind.

Dragon Rider

 At 3rd level, your rider training affords you greater versatility in the saddle. While mounted, both you and your mount gain +2 to your AC and you have advantage on saving throws made to avoid falling off of your mount.

Additionally, you can use a bonus action while within 60 feet of your mount to verbally command it to immediately move up to its movement speed towards you as a reaction. If the mount is intelligent, it may refuse this order.

Finally, mounting and dismounting only costs you 5 feet of movement, rather than half of your speed.

Dragonhide

Starting at 3rd level you call upon the legendary toughness of dragons. When you take bludgeoning, piercing, or slashing damage from a weapon attack, you can use your reaction to reduce the damage taken by an amount equal to your fighter level; your skin hardens in response to damage, momentarily appearing as tough dragon scales.

Additionally, your hit point maximum increases by 1 for every fighter level you have.

Fearful Presence

At 7th level, you can exude a frightening aura, a lesser version of the frightening presence of true dragons.

As an action, you can send out a wave of draconic fear, forcing a Wisdom saving throw (the DC is equal to 8 + your Constitution modifier + your proficiency bonus) on creatures of your choice within 30 feet of you that are aware of you. On a failed save creatures are frightened of you for 1 minute. At the end of each of their turns, a frightened creature can repeat the save, ending the effect on a success. A creature that succeeds on this saving throw is immune to your dragon fear for 24 hours.

You can use this feature a number of times per day equal to your proficiency bonus.

Wyrm's Inurement

Upon reaching 10th level in this class, you can call upon the elemental powers of dragons to empower your blows and strengthen your defenses. At the end of each long rest, choose a damage type from the following list: acid, cold, fire, lightning, or poison

Until the end of your next long rest, you have resistance to the chosen damage type, and your weapon attacks deal an additional 1d6 damage of the chosen type.

Eyes of the Dragon

Starting at 15th level, you gain the senses of a dragon, both natural and preternatural. You have blindsight out to a range of 30 feet; if you already have blindsight, add 30 feet to its range. Additionally, you gain expertise in perception checks.

Legend

At 18th level, the capstone of the dragon knight, you ascend into legend. When you use your indomitable feature, it is instead considered a legendary resistance, allowing you to automatically succeed on the relevant saving throw.

Additionally, you gain one legendary action, which you can use at the end of another creature's turn; you can use this action to make an attack with a weapon you are wielding, move up to your movement speed (or your mount's movement speed if you are mounted), or to make a perception check. You regain your spent legendary action at the start of each of your turns.