Dragon Rider

You attuned to a dragon egg and have created an unbreakable bond that gives you the following:

• You gain a dragonmark feat
  • It is up to the DM which Dragonmark you gain
• You gain a dragon hatchling companion

As well as the other features listed below 

Telepathic Link

Due to the unbreakable bond you now share with the dragon, you gain a telepathic link to the dragon companion that allows you to both communicate in either draconic or your native tongue

This link also lets both of you sense when the other is in danger or other heightened moods of emotion

It is up to the DM rather or not the link works across different planes

Dragon Life Stages

At 3rd level, the Dragon Egg hatches into a Dragon Hatchling. At this life stage, the DM controls the dragon, but the player can attempt to make an animal handling check to get the dragon to obey a command

At 5th Level, the Dragon Hatchling transforms into a Dragon Wyrmling. At this level, the dragon's actions are no longer controlled by the DM. Also starting at this level, the dragon may use an action to change its shape into that of a previous life stage while retaining all of its current stats.

At 10th Level, the Dragon Wyrmling transforms into a Young Dragon

At 18th Level, the Young Dragon transforms into an Adult Dragon

The DM will set the dragon's stats at each lifestage to ensure the best integration possible (There are Unique Dragon Variants in the Homebrew listed as "Dragon Rider Variant"

Draconic Influence

Due to the link you now share, you and your dragon will gain abilities further melding your two souls into one. These features are optional, and may also be distributed by rolling a d6 versus the leveling system listed bellow.

At 4th level, you can breath a harmless sensory effect related to your dragon's breath

At 5th level, your dragon can fold its wings into its back as if they have disappeared

At 6th level, you gain darkvision if you did not have it before, and when in use, rather you had it before or not, your eyes change to match that of your dragon's

At 7th level, your dragon gains the ability to walk upright efficiently

At 8th level, you gain the ability to grow claw like nails that deal slashing damage and add an additional 1d8 to your unarmed attacks 

At 9th level, your dragon can find your location even if you are unconscious

Additional cosmetic and/or other influences may be added by the DM (Scales grow on the player, the dragon grows hair, the two of you switch personalities occasionally, you gain the same obsessions as your dragon; etc.).  

Find Familiar 

At 3rd level, you learn the Find Familiar spell, but it only works for your dragon companion

Mount

At 5th level, mounting or dismounting a creature costs you only 5 feet of movement, rather than half your speed. In addition, you have advantage on saving throws made to avoid falling off your mount. If you fall off it, you can automatically land on your feet if you aren’t incapacitated and you fall less than 10 feet. Your dragon companion is still too inexperienced with carrying other creatures while flying, so they cannot fly while you're mounted on them.

At 10th level, it can fly at half speed with you on

At 12th level, it can use its full speed while being mounted.

Mounted Combat

At 8th level, while you are mounted, your melee weapons gain 5 extra feet to their normal reach. Also, if you make a jump from the back of your dragon, you gain a bonus equal to the dragon's strength modifier in feet for the distance of your jump.

At 12th level, while mounted, your dragon can use its breath weapon to coat your melee weapon or projectile in its element adding a 1d8 of additional magic damage equal to the elemental form of the breath.

Dragon Deaths

If your dragon were to die, you may revive them, but at a great financial cost. The ritual to bring them back must be performed for 8 hours of focus and concentration using rare components of the DM's choosing that equal 5,000gp. After each successful revival ritual, the cost of materials doubles.

After 4 hours, if the ritual is interrupted and/or concentration is broken the ritual fails and a hostile Draco is summoned instead with the materials being used up in the process. If the ritual is interrupted in under 4 hours, no hostile is summoned, but half of the materials are used up.