Oath of the Platinum Dragon

 The Oath of the Platinum is a covenant forged between paladins and Bahamut. Paladins who take this oath, often known as Platinum Knights, pledge to protect good dragons, honor his principles, and prove themselves worthy to be an Honorary Dragon. In exchange, Bahamut imparts some of its own power, allowing the paladin to assume the visage of a dragon to help strike down the evil in the world.

Tenets of Bahamut
the ancient great wyrm demands vows and services of his paladins. Draconic paladins tend to follow these core principles:
     The Dragon's Scale. Protect those who cannot protect themselves. Inaction resulting in the death of an innocent you could have prevented constitutes your failing as a paladin and will result in your fall.
     The Dragon's Wing. You are to travel far and wide to combat hus enemies and steal from their hordes. Only by flying far are you to extend your Bahamut's influence.
     The Dragon's Tooth. Slay your enemies with the ferocity of a dragon. Those who follow in your wake should feel the might of the a great wyrms through your actions.

Channel Divinity

When you take this oath at 3rd level, you gain the following two Channel Divinity options.

Breath Weapon: As an action, you can expend your Channel Divinity to exhale with the destructive breath of the mighty dragon. Your damage type is cold and each creature in the area of exhalation must make a Constitution saving throw, A creature takes 2d6 damage for each point of your proficiency bonus, or half as much damage on a successful save.

Dragon Scales: As a bonus action, you can expend your Channel Divinity to plate yourself in dragon's scales of the same color as Bahamut. For the next minute, you have resistance to cold damage. Additionally, whenever you take damage, you can use your reaction to reduce the damage taken by 1d8. If the attacker is within 5 feet of you, it then takes cold damage equal to the same amount. 

Oath Spells

You gain oath spells at the paladin levels listed.

Oath of Devotion Spells

Aura of Fear

Starting at 7th level, when a creature with a challenge rating of less than your level moves within 10 feet of you, you can use your reaction to invoke the aura of the Platinum Dragon. That creature must take a Wisdom saving throw or be frightened for 1 minute or until it takes any damage. After a creature fails its saving throw against this effect, it is immune for 24 hours.

At 18th level, the range of this aura increases to 30 feet.

Legendary Resistance

At 15th level, when you fail a saving throw, you can instead choose to succeed using your reaction. After using this ability, you can't use it again until you finish a long rest.

Favored of Bahamut

Favored of the Bahamut: You have proven to be a great warrior and defender to the Platinum Dragon. While your Dragon Scales Channel Divinity is active, you can use your bonus action to extend your damage resistance to a friendly creature you can see within 30 feet of you. While that creature remains in this range, it has resistance to cold damage along with you. You can switch this resistance to another friendly creature you can see within range as a bonus action.

Platinum Avatar

At 20th level, you can use your action to assume the perfect form of ancient dragons. For 10 minutes, you gain the following benefits:

• You sprout scaled wings from your back, which grant you a flying speed of 60 feet.
• You have immunity to the cold damage type. 
• You can use your reaction when you take damage to reduce that damage by 1d12.
• You can use your breath weapon at will. 

Once you use this feature, you can't use it again until you finish a long rest.