Bahamut

Whether you are a glorious hero of your village or a silent and discreet force of goodness, Bahamut or one of his emissaries noticed you. Maybe a songbird of golden hue landed on your shoulder and whispered the Platinum Dragon's blessings upon you. Maybe an old man held your hand to thank you for your charity. In any case, that day, you received a piece of the might of Dragons, which you are expected to put to good use.

Note: I am bad at formatting so whenever I have the time, I'll try to improve it. Any help and criticism is welcome. How are do you format a table in these text boxes? This is my first piece of homebrew so bear with the amateurism.

Expanded spell list

Bahamut lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you:

 (Until I find out how to make tables this will be shown in text)

1st level: Absorb Elements and Chromatic orb

2nd level: Dragon's breath and Spiritual Weapon

3rd level: Ashardalon's Stride and Fireball

4th level: Fire Shield and Storm Sphere

5th level: Circle of Power and Summon Draconic Spirit

Above 5th level: Fizban's Platinum Shield and Draconic Transformation

Draconic Majesty

Starting at 1st level, while you aren't wearing armor, you can add your Charisma bonus to your Armor Class.

Shining Transformation

Also at 1st level, you gain the ability to enter a form that is the pinnacle of yourself as a bonus action. While in your Shining Transformation, you gain these benefits:

• You have advantage on Charisma (persuasion) and Charisma (intimidation) checks. Your voice can boom up to 300ft should you decide it so.
• You have advantage on saving throws against the charmed and the frightened conditions, and you can immediately repeat your save if you are already affected by the condition as you transform, potentially ending it immediately.
• You gain temporary HP equal to 1d10 + your warlock level.

The transformation lasts for 1 minute, or until you become unconscious. You can transform a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Improved Pact Boon

When you obtain your Pact Boon, you gain additional benefits depending on the one chosen:

• Pact of the Chain: you can add the Faerie Dragon (younger) to your options when you cast the find familiar spell. It cannot use its spellcasting feature*. Commanding your familiar to use a breath weapon costs an action. You can only do so a number of times per day equal to half** your proficiency bonus (rounded down).  
• Pact of the Blade: you may manifest a weapon of any type you've wielded before. You may do so as if you were drawing a weapon during the attack action. You may have 2 Pact Weapons active at the same time (the one of your choice vanishes if you create a third while 2 are already active). You can also make 2 magic weapons into your pact weapons, making you unable to manifest anything other than the 2, but giving both the usual benefits.
• Pact of the Tome: while the tome is on your person, you cannot be surprised. You can use the Tome as a spellcasting focus for your Warlock spells, and it can replace costly material components not consumed by the spell, up to a value in GP equal to 50 times your Warlock level.

*The younger Faerie Dragon's spellcasting is actually not that good. You could consider upgrading colors with Warlock levels but that is too convoluted for a subclass that is already a mess, and having a familiar cast polymorph on an ally sounds a bit OP, even by the standards of this quite powerful subclass

**the system to limit uses on the site only accepts whole numbers so you'll have to limit yourself manually

Shining Beacon

As you gain in power, you can reach further into your own glory and that of the Platinum Dragon.

From 6th level onwards, when you enter your Shining transformation, you gain resistance to Fire, Cold, Poison, Acid or Lightning damage until the transformation ends. You also gain a flying speed of 30ft during your transformation, as majestic spectral wings manifest. Your Shining Transformation grants you additional benefits depending on your Pact Boon:

• Pact of the Blade: you can use Charisma instead of Dexterity or Strength for attack and damage rolls with your Pact Weapon during your transformation.
• Pact of the Chain: your familiar gains the same temporary HP as you do when entering your transformation. If there is any temporary HP left as your transformation ends, it expires.
• Pact of the Tome: You have advantage on Constitution saving throws made to maintain concentration on a spell while the transformation is active. You can also change the damage type of your spells of first level and higher to your choice of Fire, Cold, Poison, Acid or Lightning damage.

Awakened Boon

Starting at 10th level, your Boon is imbued with more potent magic.

• Pact of the Blade: Your Pact Weapon now deals 1d8 additional damage (when you hit, you choose a type between Fire, Cold, Poison, Acid or Lightning for the additional damage)
• Pact of the Chain: Your Familiar gains access to this Breath Weapon: Elemental Swirl (Recharge 5-6). Each creature in a 30ft cone must make a Dexterity saving throw, taking Xd6 damage on a failed save, or half as much damage on a successful one. X is your Warlock level, and the damage type is your choice of Fire, Cold, Poison, Acid or Lightning.
• Pact of the Tome: Spells you cast with the Tome have a +2 to attack rolls, and you have a +2 bonus to your spell save DC. In addition, once per Long Rest, you may spend an action to regain one of your Pact Magic slots.

Overwhelming Splendor

Starting at 14th level, your Shining Transformation reaches its absolute best. While in your shining transformation, you become immune to the charm and frightened conditions (they end on you if you enter the transformation under one of them), and allies within 30ft have advantage on saving throws to resist or end those conditions. Whenever a feature granted by this subclass allows you to chose between Acid, Cold, Fire, Lightning or Poison, you may now also choose Radiant if you are in your Shining Form.

Ascendant Boon

Starting at 14th level, when the situation calls for it, you may push yourself to your limits, channeling immense power through your Boon:

• Pact of the Blade: As a bonus action, you may channel power through your Pact weapon (it can be the same bonus action you use to enter your Shining transformation). For 1 minute, your pact weapon deals yet an additional 2d8 to its damage rolls (of the same type as the additional damage from your Awakened Boon feature)
• Pact of the Tome: When you cast a spell of 1st level or higher, you may channel power through your Book. When you do so, consider the spell as if it were cast at a level equal to half your Warlock level (rounded up). If this spell requires you to concentrate, your concentration cannot be broken by damage for this spell.
• Pact of the Chain: As an action, you may summon a great draconic ally to aid you in your woes. You summon a Draconic Spirit, as if you had cast the Summon Draconic Spirit spell at a level equal to half your Warlock level (rounded up). When you do so, the spirit stays for 1 minute (no concentration required).

You may only use this feature once. To regain it, at the end of a long rest, roll 1d6. On a 5 or 6, it recharges (as with breath weapons)