As a Drake Knight, you are attempting to master the art of fighting alongside your Drake companion. Through the time you'll spend with him or her, you may not only find a trusty steed, but a reliable battle companion. In return for your care and guidance,  you'll find that your guardian drake will return your generosity in kind. In world that you seek to conquer or defend, there will be no other being you can trust more to watch your back.

Dragonic Kinship

Dragonic Kinship.

When you choose this archetype at 3rd level, you learn how to speak, read, and write Draconic. Additionally you become proficient in the animal handling skill; whenever you make a Wisdom(Animal Handling) check to interact with Drakes you can add  your proficiency bonus to the check. Finally, mounting or dismounting your drake only costs 10 feet of movement instead of half of it.

Guardian Drake and Battle Bond-Unlikely Alliance

Guardian Drake.

Starting at 3rd level, you can preform a ritual by spending several days, 50 gold pieces worth of chemicals (such as those found in the alchemist's supplies) and requires 10 pounds of fresh draconic scales of the same chromatic type(which you've possibly had since the beginning of your journey in preparation for this if you had chosen Fighter as your starting class level should your DM allow it so), a large amount of fresh meat, and an iron cauldron. At the end of the several days when the process is complete, a halfling-sized egg emerges from the cauldron and is ready to hatch within a few hours. A Guard Drake(whose stat block will be provided, via a link down below) is fully grown within two to three weeks and can be trained in the same length of time. In time the Guardian Drake  grows large enough to serve as your steed. 

 The Guardian Drake's chromatic color depends on that of the scales used during the ritual be they; red, blue, green, black, or white. Your drake gains all the benefits of your Battle Bond- Unlikely Alliance feature. You can only have one drake at a time. If your drake is ever slain, you can ritually resurrect it by spending 4 hours during a period of long rest, 50 gold worth of alchemical supplies, and its body to revive the Guardian Drake. In the worst case scenario where the Guardian Drake's body is no longer available, you must repeat the process of creating a Drake once again in order to call forth the spirit of the Drake to enter a recreation of its body, or to create a new body for it during the resurrection process. if you use this ability to return a former drake to life while you have a different one under your command, your current drake leaves your service and is replaced by the restored drake.

A newly hatched guard drake imprints upon creature who summons/ resurrects it, establishing an aggressive but trusting bond with that individual.

https://imgur.com/53QOdBv

The Drakes physical characteristics, (aside from it's chromatic color, and some inate features which come with that color) are entirely up to you. ie. tails, claws, teeth, horns, etc.

Battle Bond-Unlikely Alliance .

At third level, your drake gains a variety of benefits while under your command. While mounted it loses it's Multi-Attack feature, it moves/acts on your initiative, you can order it to move based on it's speed(not taking away your Action or Bonus Action), whenever you make a Melee Weapon Attack as your attack option, your drake can roll to attack as your bonus action; on hit the damage die for this bonus attack is 1d4 slashing/bludgeoning damage.

However whenever you to take the attack option, you can give up your attacks to command the drake to make a attack in your stead by using the attack options listed in it's stat block;  in this case you can use your bonus action to add your WIS modifier to your Guardian Drake's damage calculation.

Whilst using your second wind feature, you can choose to have the drake regain hit points instead of yourself. If you  are incapacitated, the drake  will do it's best to protect you and itself, using the abilities it has listed in it's stat block, and any abilities gained under your care.

Your Guardian Drake has abilities and game statistics determined in part by your level. your drake uses your proficiency bonus instead of it's own, and in addition to the areas where it would use the proficiency bonus, it will also be added in order to calculate it's AC. Your drake, gains proficiency in two skills of your choice from the following list: Acrobatic, Athletic, Survival, Perception, and Insight. It also  becomes proficient in two saving throws of your choice.

For each level after third level, your drakes gain additional hit die and increase it's hit points accordingly.Like any creature, your drake can regain it's hit die during a short rest and long rest, when treated with a healing spell, or under the effects of a potion equal to or more potent than a Potion of Healing . Whenever you gain the ability score improvement class feature, your drakes abilities also improve any ability score by 1. Your drake cannot increase it's ability scores past 20, unless affected by other magical means.

Your drake shares your alignment, has one personality trait and flaw of your choice, and only understands verbal commands spoken in draconic.

Chromatic Drake-Blue

Blue. A Blue Guardian Drake has a burrowing speed of 15 feet, gains an additions 10 feet of flying speed when reaching 15h level, and is resistant to lighting damage. In addition, whenever attacking a flying creature, the Guardian Drake and it's master have advantage so long as thier within 10 ft of each other.

 

Chromatic Drake-Green

Green. A Green Guardian Drake is amphibious; it can breathe air, water, and has a swimming speed of 15 feet. it is also resistant to poison damage. In addition whenever the Drake and its master attempt to make a Stealth check within Forest and Grassland environments while thier within 10 feet of each other, they have advantage.

 

Chromatic Drake-Red

Red. A Red Guardian Drake has a climbing speed of 15 feet, gain an additional damage die to thier Elemental Discharge when reaching 10th level and are resistant to fire damage. In Addition, whenever you find currency as a result of looting an enemy or dungeon while your Drake is within 10 feet of you, you find 50% more of what you originally would have found.

 

Chromatic Drakes-Black

Black. A Black Guardian Drake is amphibious, it can breathe air or water, it has a swimming speed of 15 feet, and is resistant to acid damage. In addition whenever an ally attempts to make an Intimidation check against a target while the Drake is seen visibly within 15ft, they have advantage.

Chromatic Drake-Undead (Work in Progress/Unfisinished)

Undead. A Undead Guardian Drake is amphibious. As a result of its undead nature drakes basemovment speed is decreased by 10 feet, it gains a swimming speed of 10 and flying speed of 20 instead of 30 when reaching 15th level.

As an undead, the drake has an immunity to Cold damage, and resistance to slashing and piercing damage. Whenever the drake levels up, increase its health points by 2d10 instead of the standard 1d10. As a undead the drake is immune to exhaustion, and does not require the need for rest or the need to eat.

The drake gains a weakness to fire and radiant damage. While it can regain it's hit points via a short or long rest, it cannot health via the use of healing spells or health potions.

Undead Presence

As a undead, it's presence on this world is unnatural. Whenever a non-hostile creature of neutral or good alignment gazes upon this creature for the first time (unless they are present during its summoning or revival) they must pass a DC 13 Intelligence saving throw to recognize is as a summoned mount under the  control of a master. Failure to pass the saving throw results in the creature responding to the Undead Presence in the best way seen fit by the Dungeon Master; be it the decision to run away, call the guards, attack on site, or etc.  

Chromatic Drake-White

White. A White Guardian Drake has a burrowing speed of 15 feet and a climbing speed of 15 feet, and is resistant to cold damage. In addition whenever the Drake or it's master attempt a strength check while they are within 10 feet of eachother, they have advantage on the roll.

Battle Bond-Predatory Influence

The fighting instincts you've witnessed within your drake influence your combat style, when separated from your Drake companion at a distance of 30 feet or greater, (or in cases where the Drake is deceased) you gain the following abilities at the corresponding levels.

Battle Bond-Predatory Influence

3rd Level: Groveling Prey

7th Level: Of Might and Malice

10th Level: Draconic Echoe

15th Level: Reckless Abandon

18th Level: Dragon Aura

Dragon Tactics

Starting at 7th level, the additional damage die added whenever you use your bonus action to command your drake to attack after attacking yourself while mounted provided by the Battle Bond-Unlikely Alliance feature is increased to 1d6 instead of a 1d4.  Whenever your drake attacks in your stead while your mounted, the additional damage provided by your WIS modifier is joined by an additional 1d4 die roll. In addition the  Drakes attacks count as magical for the purpose of overcoming resistance and immunity to piercing, bludgeoning and slashing damage from non-magical weapons.

 

Elemental Breath

Red: Fire

Blue: Lighting

Green: Poison

 Black: Acid

White: Cold

Undead: Necrotic

Storm Rider

Beginning at 15th level, your drake has developed a stronger link to it's draconic heritage, which results in manifesting a pair of large dragon-like wings; your drake gains a flying speed of 30 feet. Whenever your drake makes an melee attack, the damage die is increased by an additional damage die roll.In addition, being stunned, paralyzed, or knocked prone doesn't knock you off your mount. Your dragon cannot fly while encumbered.

Element Blitz.

Once per long rest as an action while youre mounted, your drake can envelope itself in an aura of energy based on it's chromatic type and charge at its opponent. Choose a single target standing within the drakes available movement speed, the target must succeed a DC 8 (+ the drakes proficiency bonus + the drakes Strength modifier) Dexterity saving throw or take damage equal to 2d10 (+ an additional 1d10 for every ten feet of movement speed the drake uses to reach the target, ) and be knocked prone ,or remain standing while taking half as much damage incase of a successful saving throw. The Guardian Drake, and the rider(if one is currently mounted) both take damage equal to a quarter of the total damage die rolled.

Draconic Fusion

At 18th level the bond that binds you and your mount is so strong that it allows you to magically meld into a single being manifesting as a creature comprised as your drakes element type. As a bonus action while youre mounted, you can fuse with your drake, becoming a single creature. You still retain the mental capacity you enjoyed as a person, but are unable to communicate. While fused, your combat prowess is determined by splitting your stats between yourself and that of your Guardian Drake. This transformation lasts for 2 hours, until your HP is taken down to zero, or until you decide end the transformation via the use of an action.

While fused, You take the higher of the two Armor Classes between yourself and your drake.To decide your total HP: add both of the current HP of yourself and your drake at the time of fusion and divide by two rounding down to the nearest whole number.  Your attributes are decided by adding both the attributes of yourself and your drake's and dividing by two rounding down to the nearest whole number. Your movement speed capability is that listed within your drakes stat block. Your skill Proficiencies are that of your drakes, and your saving throws are that of yourself.

You obtain damage immunity to the element type of your drake, plus any additional immunities or resistances that you may of both had prior to the transformation, but you also gain any weaknesses you both of had as well.

You retain your Fighter Classes extra-attacks but attacks themselves are limited to the attack options provided in the Guardian Drake Stat Block.If a hostile enemy starts it's turn within 5 feet of you, they take 1d6 points of damage based off the element type of your drake.

If you had used your single Element Breath and/or Element Blitz option between long rests prior to your transformation, you regain your uses during this fusion. The damage your Element Breath and Element Blitz options are increased by 2d6 and 2d10 respectively whilst transformed via your Draconic Fusion.

Once your transformation ends you obtain a minimum of 3 Exhaustion Points, plus an additional exhaustion point for your uses of Element Breath or Element Blitz options whilst in this form.