Eyes wide open
Tired of Warlocks? Today is your lucky day! Here's a Paladin subclass that will hate the ever-loving crap out of their patron and zap all of their fiendish, fey and otherworldly friends into oblivion with glee! With a remit to keep everyone safe from anything that comes from beyond the stars (which translates to anything from a different plane, you're not just hating on Yog-Sothoth) the Oath of the Watcher Paladin is ready and waiting to do heinous amounts of damage to any creatures not from this neighbourhood.
Each of the subclass features below includes a brief summary of the relevant rule, but to see them in full you can download the Unearthed Arcana article for free from the Wizards of the Coast website, here.
Oath Spells
Paladins are meant for smiting, right? Right? Wrong. While half-casters have much more limited resources than full casters in terms of spell slots, this subclass has been built with actually using your spells instead of just burning your slots for smites in mind.
First up, as soon as you take this oath, you get Chromatic Orb. Depending on what you're fighting, that means that this spell is just as effective as smite but at a 90 foot range. Then, as your game unfolds, you get access to Counterspell when you reach 9th level and Banishment at 13th level. Both of these are impactful weapons in your arsenal, with Banishment in particular playing to the flavour of the class. What says galaxy defenders more than straight up sending something back to its home plane without having to even swing your sword?
Just to cap things off, at 17th level, you'll gain access to Hold Monster. Can't banish it? Paralyze it. Then watch as your friends critical hit it in the face until it gives up and keels over. Job done.
Channel Divinity - 3rd Level
Watcher's Will
You and a number of other creatures within 30 feet gain advantage on Int, Wis and Cha saves for 1 minute.
Watchers will what? They'll what? Come on, seriously, what?
The answer is they'll give anyone an improved chance at resisting some particularly nasty spells. It's not often that characters will be called on to make Intelligence or Charisma saving throws, but Wisdom saves are ten a penny, for a variety of reasons. If you're facing off against a bunch of mages then this will be worth its weight in gold. (Well... more than its weight in gold because it's a concept, and they don't really weigh anything...)
Abjure the Extraplanar
Turn elementals, fey, fiends or aberrations within 30 feet if they can hear you and they fail a Wis save.
Good luck telling the DM you want to use this feature if your party is into boozy D&D sessions! Here's a hot take for you – turning is one of the finest forms of control, because it robs creatures of their actions as well as making them run away from you. Begone, you pesky pixies!
Aura of the Sentinel - 7th Level
Your Cha bonus is added to your initiative roll. One other creature of your choice within 10 feet (30 feet at 18th level) also gets this bonus.
Sometimes it's just small things that really bring out the character of a subclass and, for me, this falls into that category. If you've taken the Oath of the Watcher... doesn't it seem logical that you would be ready for battle almost all of the time? Adding your Charisma bonus to your initiative roll is a big deal for Paladins, being as it's very easy for them to deliberately dump their Dexterity stat and not care that it's low. When your armour's thicker than a Challenger tank and you hit a home run with every swing of your weapon, you usually tend not to care too much that you're going to be taking your turn after the monsters. Getting to the top of the initiative tree is a big deal, especially once you've picked up Banishment. Why let the nasty monsters have a chance to hurt your friends before you zap them back to their own reality?
But wait! This coupon is good for redemption not just for you but also for one (1) friend of your choice! Is there another slowcoach in your ranks? Or do you want to help your Bardic chum try to break the record for highest initiative roll? Whichever you prefer, the power is in your hands!
Vigilant Rebuke - 15th Level
Whenever you or a creature you can see within 30 feet passes a save against a spell, you can use your reaction to deal damage to the caster.
This is a very powerful ability that amps up a long way when used in combination with Watcher's Will. Dealing 2d8 + Charisma bonus damage to a creature is not small potatoes. I had to read this feature twice when the article came out, because I felt like I'd missed reading that you can use this feature a number of times equal to your Charisma modifier. Except I didn't. Because you can't. You can just use it every single round. Every. Single. Round.
Sure, you can only use it once per round, but if your big bad evil guy is a caster that likes some of the more gnarly spells (or who was planning on taking control of one of your party members by warping their feeble minds to their nefarious will) then you've just given them a huge uphill battle to fight.
The best part about it is that if they target more than one person with a spell (say with a Fireball), you have an increased chance of being able to fire this feature off. There is also no range on the damage you deal – it shouldn't be hard for you to stay within the required 30 feet of a party member, but if the caster that's shooting spells at you is at maximum range (even over 100 feet), you can still use this feature.
Is this situational? Yes. Does it seem totally broken against magic users? Yes. Would I limit the amount of times it can be used per long rest or stick a range restriction on it? Possibly. But hey, this is what Unearthed Arcana is all about, isn't it? Aim for the stars, and if things need to be nerfed then it can happen before they're made official. OP or not (in my opinion), I love the idea of this feature, even as a deterrent!
Mortal Bulwark - 20th Level
For 1 minute you gain truesight (120 feet), have advantage on attack rolls against elementals, fey, friends and aberrations, and you have a chance to banish them if you successfully hit them.
Wash your mouth out! Oh, Bulwark!
As a capstone, this is perfect. Ten rounds of hell-for-leather banish the things. Truesight will help you to wheedle out those pesky fey that think they can get away with appearing non-fey too. The idea of a Paladin wading through a group of fiends, causing one of them to disappear every time they strike true with their sword is pretty cinematic, and this is bound to give you some epic memories.
Conclusion
This is a great idea, from start to finish. It sets itself nicely apart from other Paladins and finally gives you a reason to cast spells instead of waiting for a critical hit that lets you unload a mega-smite. Given that your subclass features rely on it, it might even be worth juicing up your Charisma score as a main focus at early levels (although it's worth making sure your Strength isn't appalling) so that you can fully take advantage of them. Your level 20 feature will definitely benefit from having a high Strength bonus behind it so that your chances to hit your enemies are nice and high. However, the nasty, gribbly monsters you'll be poofing out of existence will find it more difficult to makes their save the higher your Charisma is – so if the groundwork for that is already laid then you're laughing.
And the DM is probably crying...