Inspired by Homebrewmindflayer, who was in turn inspired by Yamana_Eaji, who was in turn inspired by actual unearthed arcana. On May 12, I'll release VRUA 1 v1. After people look at it, I'll release a copy of what they tell me modified version.

First up: Under(dark) the Sea

Underdark Subclass (2)

Sea Subclass (1)

Underdark Feat (1)

Sea Subclass (1)

More Van Richten!  Also, I like the idea of more underdark.  

Quote from Yamana_Eajii >>

More Van Richten!  Also, I like the idea of more underdark.  

 It definitely should get more love from WotC

hope to see this soon

Quote from Bluepanther512 >>

Quote from Yamana_Eajii >>

More Van Richten!  Also, I like the idea of more underdark.  

 It definitely should get more love from WotC

 I am so excited and disappointed.  For me, it is already May 12th.  That's just geography!

Sorry, I had to address that issue.  Quirks of living in the far South East!  

Also, would it be okay if I like some of your ideas for the underdark to take some of them for the campaign I am making?

Sure. I'm just making this for fun after all :)

FYI, I live in NA CST

looks pretty cool, I'm always exited to see more homebrew!

I'm glad people are inspired by me, it means a lot. I'm looking forward until your next homebrew! 

:)

First up! Paladin's Oath of the Dark Praiser

1,1,1,1 left :)

Can I give you feedback? overall, I like it, but there are a few things that need a bit of polishing up.

Sure :). Sharing and Improving, thats the point.

Fighter's Martial Achetype, Deep Warrior!

Quote from Bluepanther512 >>

First up! Paladin's Oath of the Dark Praiser

1,1,1,1 left :)

Oath:

I will help the spider queen. (or other underdark god)

I will not accept brightness.

I will show them the dark.

Strength before weakness.

Spell List:

3rd: Arms of Hadar, Hex

5th: Darkness, Nystul's Magic Aura

9th: Bestow Curse, Animate Dead

13: Gaurdian of Faith (necrotic), Phantasmal Killer

17: Hallow, Modify Memory

Channel Divinity

Guided Strike- You may add +10 to an attack. You may do this after you roll but before if you know you'll hit.

Darkness Incarnate- You gain the effects of the invisibility spell 

Dark Aura

Bright light becomes dim light dim light excluding dim light created by this becomes dark for 10 feet around you.

Praise the Dark

You power up your attacks whilst in the dark. All advantage attacks take the highest of 3 dice when you are in darkness. You can turn invisible for four rounds as a reaction once per short rest.

Dark Devil

You take an a black, misty, form of a devil for 1 minute once per dusk. Your Dark Aura increases to 50 feet for the duration and you gain a 30 foot flying speed

•  Firstly, you need to add more description to darkness incarnate channel divinity. how long does it last? does it take an action to active like the normal invisibility spell, or does it take something else (bonus action, reaction, minute, ect). does it take concentration or not? things like that.
• Secondly, dark aura could e a bit weak compared to some of the other paladin auras. in addition, can you choose to not activate it, or do you have to keep it on? (currently how it its written, you always have to keep it on, but I personally think you should be able to turn it off).
• Thirdly, for praise the dark, you need to specify that's it's only you that gets to roll the three dice in darkness. (how it is written currently, everyone gets to). and the for second part of praise the dark, you need to specify when you can use this reaction. (when you take damage maybe?)
• Next, Dark devil is a bit weak, maybe make it a bit stronger.
• Lastly, you need top say which level each feature is for.

Quote from HomebrewMindFlayer >>

Quote from Bluepanther512 >>

First up! Paladin's Oath of the Dark Praiser

1,1,1,1 left :)

Oath:

I will help the spider queen. (or other underdark god)

I will not accept brightness.

I will show them the dark.

Strength before weakness.

Spell List:

3rd: Arms of Hadar, Hex

5th: Darkness, Nystul's Magic Aura

9th: Bestow Curse, Animate Dead

13: Gaurdian of Faith (necrotic), Phantasmal Killer

17: Hallow, Modify Memory

Channel Divinity

Guided Strike- You may add +10 to an attack. You may do this after you roll but before if you know you'll hit.

Darkness Incarnate- You gain the effects of the invisibility spell 

Dark Aura

Bright light becomes dim light dim light excluding dim light created by this becomes dark for 10 feet around you.

Praise the Dark

You power up your attacks whilst in the dark. All advantage attacks take the highest of 3 dice when you are in darkness. You can turn invisible for four rounds as a reaction once per short rest.

Dark Devil

You take an a black, misty, form of a devil for 1 minute once per dusk. Your Dark Aura increases to 50 feet for the duration and you gain a 30 foot flying speed

•  Firstly, you need to add more description to darkness incarnate channel divinity. how long does it last? does it take an action to active like the normal invisibility spell, or does it take something else (bonus action, reaction, minute, ect). does it take concentration or not? things like that.
• Secondly, dark aura could e a bit weak compared to some of the other paladin auras. in addition, can you choose to not activate it, or do you have to keep it on? (currently how it its written, you always have to keep it on, but I personally think you should be able to turn it off).
• Thirdly, for praise the dark, you need to specify that's it's only you that gets to roll the three dice in darkness. (how it is written currently, everyone gets to). and the for second part of praise the dark, you need to specify when you can use this reaction. (when you take damage maybe?)
• Next, Dark devil is a bit weak, maybe make it a bit stronger.
• Lastly, you need top say which level each feature is for.

 There is one thing that you are missing- If your opponent dosen't have any vision besides usual, you can't see in the dark, giving you advantage.

https://www.dndbeyond.com/feats/620735-lightless-vision

Woo underdark feat just need to finish the seas

Quote from Bluepanther512 >>

https://www.dndbeyond.com/feats/620735-lightless-vision

Woo underdark feat just need to finish the seas

 a bit of boring feat maybe they can also gain a minor secondary sense with their darkvision area (maybe you can sense celestials as blind points of light.)

https://www.dndbeyond.com/feats/620756-lightless-vision

Quote from Bluepanther512 >>

https://www.dndbeyond.com/feats/620756-lightless-vision

 sorry for the late response but you may want to fluff up to wording on ¨you can sense good aligned creatures¨ (does it tell you if their is a good aligned creature within sight?does it tell you if a visible creature is good?Can you sense invisible creatures using it?).I Would also appreciate some flavor text.

Quote from Bluepanther512 >>

Fighter's Martial Achetype, Deep Warrior!

The warriors of the underdark, they are the defenders of underdark villages. They are usually the more elite guards adventurers face.

3rd: Underdark Adept

You gain the Natural Explorer (underdark) feature. You are good at traversing your home terrain as you have been on the move there your entire life.

7th: Sneaking in Dark

All your attacks have advantage in the dark.

10th: Deep Seer

You gain a blindsight of 20 feet. Your time as a guard has attuned you to the dark and you've become truly attuned to your surroundings.

15: Improved Critical

You crit on a 19 or 20.

18: Life Before Death

When you reach 0 hit points, you have one extra round before you go down if you still have 0 hit points and roll death saves.

 
A few comments here. First, I don't feel that the natural explorer ability is well suited to take the 3rd-level spot here. The first subclass ability is meant to define the subclass and change their playstyle. The natural explorer ability itself is so lousy that TCoE had to essentially retcon it away. The 7th-level ability is also super powerful. In the darkness, it's more powerful (by far) than the improved critical feature. I'm happy with the 10th-level ability. It's somewhat deprecated if the character has darkvision. I'd improve it further. The 15th- and 18th-level features are fine, but I don't see how they reflect the archetype. The 18th-level feature is meant to be a capstone of the archetype.

Quote from Bluepanther512 >>

Fighter's Martial Achetype, Deep Warrior!

The warriors of the underdark, they are the defenders of underdark villages. They are usually the more elite guards adventurers face.

3rd: Underdark Adept

You gain the Natural Explorer (underdark) feature. You are good at traversing your home terrain as you have been on the move there your entire life.

7th: Sneaking in Dark

All your attacks have advantage in the dark.

10th: Deep Seer

You gain a blindsight of 20 feet. Your time as a guard has attuned you to the dark and you've become truly attuned to your surroundings.

15: Improved Critical

You crit on a 19 or 20.

18: Life Before Death

When you reach 0 hit points, you have one extra round before you go down if you still have 0 hit points and roll death saves.

 Again flavor text and fluff up some wording.You already have advantage on attacks made against creatures that cannot see you the 7th level feature is barely better then that.I do not see how improved critical and life before death have to with the theme of the subclass.