Draconic Mount

Some dream of soaring through the clouds atop a mighty draconic steed, feeling the wind on their faces, afraid of nothing. The dragonrider doesn’t simply dream of this life—he leads it. Characters of all classes may become dragonriders, though the most common are barbarians, fighters, paladins, and rangers.

The dream mount for many characters is a dragon. While other flying creatures might be cheaper or easier to train as mounts, nothing beats the look of awe from friends and foes when they see you swoop in astride a mighty draconic steed. There are two methods of getting a dragon as your mount: raising the dragon from youth or negotiating with a fullgrown dragon. The first may be easier and cheaper, but requires far more time. Each method is discussed later in this section As strong, quadrupedal creatures, dragons can carry a lot of weight, even in flight. A dragon can carry a rider while swimming, but not while burrowing.

This feat contains a number of bonuses based on the Dragonrider prestige class from 3e.

DRAGON Mount

Large Dragon

Armor Class 15 (natural armor)

Hit Points 18 (2d10+8)

Speed 40 ft.; climb 20 ft, fly 80 ft.

STR

19 (+4)

DEX

12 (+2)

CON

17 (+3)

INT

16 (+3)

WIS

13 (+1)

CHA

15 (+2)

Senses darkvision 60 ft., passive Perception 12

Languages understands the languages you speak, Draconic

Challenge — Proficiency Bonus equals your bonus

Dragon Health: Your dragon has a hit die count and proficiency equal to it's rider.

Dragon Stats: Add your proficiency to your dragon's Attack Rolls, Damage Rolls, and saves that you are proficient in. You can use the stats for Young [Color] Dragon or build them like you would a character. 

If making your own stats for your Dragon Mount use the formula AC=10+DEX+CON

If making your own stats for your Dragon Mount increase ability sore or add a feat on levels 4, 8, 12, 16 and 19.

Dragon Rider Link: You are mentally linked to your dragon. You can communicate silently with each other and can't be intercepted. The downside of this is any mental effects or psychic damage taken are shared between rider and mounted. This link requires an attunement slot but has no prerequisites.

Note that although your messages are transmitted in common your dragon's thoughts are more primal. Your dragon will transmit their thoughts in the form of emotions, feelings, and single words.

 Draconic Magic: A Wizard or Dragon Trainer can teach your dragon spells from the wizard spell list. Use the Wizard spell slot allotment for your level to determine your dragon's spell slot.

Draconic Skills: A Dragon Trainer or another Dragon Rider can teach your dragon a variety of skills.

"I'm on a dragon, your argument is invalid": Use your dragon's CHA bonus in addition to yours when in close proximity to your dragon. This won't apply to Dragon Domain Clerics, Dragon Riders, or non-humanoids.

Draconic Temperament: 

Metallic: Metallic Dragons love people and cooperating with them. Metallic partners enjoy following orders and working to aid their partners and allies. Their almost domestic disposition makes them a common choice.

Crystal: Aloof and stubborn Crystal Dragons happily serve their partners and very few beyond that. While a well trained one will follow orders their stubbornness might warrant a few repeats. The training issues are compacted by their rarity and the scarcity of those with experience with them.

Chromatic: Feral and wild these dragons value strength. While they will serve a rider who's earned their respect they are very reward motivated and will rarely act without seeing a gain for them or a promise of praise. Beware their egos.

Diet: Dragons are omnivores with a preference for meat. Due to its mass your dragon will need to eat the equivalent of 3x a medium humanoid's diet.

 Mounted Spellcasting: A Dragon Rider has a +5 bonus on Concentration checks made to cast a spell while riding a mount

Dragon Initiative: Because of training and, your link, your dragon will always follow immediately after you in Initiative order.

Actions

Multiattack. The dragon makes two attacks: one with its bite or two with its claws.

Bite. Melee Weapon Attack: STR+Prof to hit, reach 10 ft., one target. Hit: 5 (1d10) piercing plus STR damage plus 3 (1d6) [element] damage.

Claw. Melee Weapon Attack: STR+Prof to hit, reach 5 ft., one target. Hit: 3 (1d6 ) slashing damage plus STR.

[Element] Breath (Recharge 5–6). You can use your action to exhale destructive energy. Your draconic ancestry determines the size, shape, and damage type of the exhalation. When you use your breath weapon, each creature in the area of the exhalation must make a saving throw, the type of which is determined by your draconic ancestry (Line for Chromatics, Cone for Metalics). The DC for this saving throw equals 8 + DEX+ your proficiency bonus. A creature takes 2d6 damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level.