Base Class: Cleric
The Entropic domain is the domain of one deity in particular: Entropy. As the goddess of indulgence, curiosity and entertainment, she encourages the same of her followers. Entropy is a unique deity in that she often and readily interacts with mortals of all kinds, spending the majority of her time on the material plane. Because of this, clerics of the Entropic domain are likely to have personally met Entropy; or at the very least one of her aspects.
Divine Gift
When you choose this domain at 1st level, Entropy bestows you with a greatsword created in the image of one of her own two greatswords. Choose either a Liberating Blade or a Chained Blade. Your choice determines the greatsword's extra damage type.
The greatsword is a legendary magical weapon with a +3 bonus to attack and damage rolls.
While you hold the weapon, you are proficient with greatswords, and you can use it as a spellcasting focus for your cleric spells.
When making an attack with the weapon, you can choose to use Charisma for your attack and damage rolls, and it deals an extra 3d20 damage on hit. The extra damage is necrotic if you chose a Chained Blade, or radiant if you chose a Liberating Blade.
Charismatic Devotion
Also starting at 1st level, when you cast a cleric spell or cleric cantrip you use Charisma as your spellcasting ability instead of Wisdom.
Channel Divinity: Legendary Swiftness
Starting at 2nd level, you can use your Channel Divinity to move with exceptional speed, mimicking Entropy herself. When another creature you are aware of takes an action, you can use your reaction to move up to your speed and take an action of your choice.
Channel Divinity: Lustful Aura
Also starting at 2nd level, you can use your channel divinity to emit a seductive aura. Choose a number of creatures equal to double your charisma modifier within 60 feet of you. Chosen creatures must make a wisdom saving throw. On a failed save, affected creatures are charmed by you for 1 hour or until it takes any non-consensual damage. While charmed, a creature views you as exceptionally sexually attractive, is willing to have sex with you, and may be convinced to act in a certain way in exchange for sexual favors at the DM's discretion.
Charismatic Defense
Beginning at 6th level, while you are wearing no armor and not wielding a shield, your AC equals 10 + your Dexterity modifier + your Charisma modifier. Additionally, when you would make a Wisdom saving throw, you can choose to make a Charisma saving throw instead.
Legendary Vulnerability
If a creature within 60 feet of you succeeds on a saving throw, you can cause that creature to fail instead. You can use this feature a number of times equal to half your Charisma modifier (rounded up, minimum of once, maximum of 5 times), and you regain all expended uses when you complete a long rest.
Divine Strike
At 8th level, you gain the ability to infuse your weapon strikes with divine energy. Once on each of your turns when you hit a creature with a weapon attack, you can cause the attack to deal an extra 1d8 damage of the weapon's type. If the weapon is your greatsword granted by Divine Gift, the extra damage of this feature is of the same type as the greatsword's extra damage. When you reach 14th level, the extra damage increases to 2d8.
Spell Replication
At 17th level, your devotion to Entropy allows you to replicate the effects of spells in the same way she does. You can replicate any spell of you choosing that you has seen casted before. You require no components to do so, you are not considered to be casting a spell, and the subsequent effect(s) are not considered to be magical or a spell effect (and therefore cannot be dispelled). Otherwise, the spell functions as normal. To replicate a spell, it must be of a level you could normally cast, and you must expend a spell slot of the appropriate level.