Academy Dragon Knight

The Dragon Knights are paragons of valor and leadership who partner with dragons. Such knights aspire to protect the innocent and rally fellow adventurers to the causes of justice and freedom. Although the Dragons were originally founded by King Vargus, new recruits are enlisted from any realms where chivalry is in abundance, given they graduate from the King's Academy. Characters with this subclass are special among the order. Unlike the old Dragons Knights, who partner with dragons who’ve already reached adulthood, an Academy Dragon Knight character bonds with a dragon hatchling. This bond irrevocably transforms both dragon and knight, allowing the dragon to grow in strength alongside its partner knight.

Knightly Envoy

You learn one language of your choice, which you choose from the language tables in the Player’s Handbook.
Additionally, you can cast the Comprehend Languages spell but only as a Ritual. Charisma is your spellcasting ability for it.

Dragon Companion

You are bonded with a dragon hatchling that serves as your dragon companion and uses the Dragon Companion stat block. The dragon is Friendly to you and your allies and obeys your commands.

Draconic Element When you take this subclass, chose a damage type listed in the Draconic Element trait  of the Dragon Companion's stat block. The dragon's general cosmetic characteristics, such as color, scale texture, or any visible effects of its Draconic Element should coincide with the damage type chosen.

The Dragon in Combat. In combat, the dragon acts during your turn. It can move and use its Reaction on its own, but the only action it takes is the Dodge action unless you take a Bonus Action to command it to take the Rend action or some other action. You can also sacrifice one of your attacks when you take the Attack action to command the dragon to take the Rend or Elemental Breath attack action. If you have the Incapacitated condition, the dragon acts on its own and isn’t limited to the Dodge action.

Resurrecting the Dragon. If the dragon companion has died within the last hour, you can take a Magic action to touch the dragon and expend a use of your Second Wind. The dragon returns to life after 1 minute with all its Hit Points restored. Otherwise, you can perform a 1-hour ceremony to resurrect the dragon; this ceremony can be performed as part of a Short or Long Rest.

https://www.dndbeyond.com/monsters/6795119-dragon-companion-hatchling

Draconic Element

When you first select this subclass at Level 3, choose a damage type: acid, cold, fire, lightning, or poison. The chosen type determines the dragon's immunity and the damage of its Rend and Elemental Breath attacks.

Dragon Rider

You and your dragon gain the following benefits.

Dragon Mount. The dragon grows to Medium size. You can use the dragon as a mount if you are Medium or smaller, but while you’re riding it, the dragon falls at the end of a turn if it’s airborne and the only thing holding it aloft is its Fly Speed. It takes you only 5 feet of movement to mount or dismount the dragon.

Improved Attacks. Damage from the Dragon Companion's attacks ignore Resistance to the damage type associated with the Draconic Element selected at Level 3. The dragon’s Elemental Breath attack becomes a 30-foot Cone. When a creature fails its saving throw against that Breath Attack, the creature also takes an additional 2d6 damage of the the type chosen for the Draconic Element.

Shared Second Wind. When you use your Second Wind to regain Hit Points, the dragon also regains Hit Points equal to 1d6 plus your Fighter level.

Rallying Surge

When you use your Action Surge, you can choose up to three allies within a 30-foot Emanation originating from you. Each ally can take a Reaction to use one of the following options.

Advance. The ally makes one attack with a weapon or an Unarmed Strike. If your dragon is one of the allies using Advance, the dragon can make one Rend attack.

Retreat. The ally moves up to half its Speed without provoking Opportunity Attacks.

Chromatic Pinnacle

You and your dragon companion gain the following benefits.

Superior Mount. The dragon grows to Large size, and both its Speed and its Fly Speed increase to 40 feet. Additionally, the dragon no longer falls at the end of a turn if airborne while you’re riding it.

Empowered Rend.  The dragon's Rend attack deals an extra 1d6 damage of the type chosen for its Draconic Element.

 

Enduring Commander

You and your dragon have Resistance to the damage type selected with Draconic Element at Level 3.