Winter Walker Review:
Lore: I made an arctic ranger subclass pretty much thematically identical to this one over 4 years ago, and there's also a good amount of mechanical overlap between the UA subclass and my homebrewed one. Mine was even called the Frost Strider, which is pretty similar to Winter Walker. I'm not saying they stole my idea, just that I was able to predict a subclass idea WotC eventually published before they made it. It's happened a few times before.
Anyways, I clearly like the idea of an arctic ranger, because I made one already. This version is definitely better balanced and less reliant on the environment than mine was.
Frigid Explorer: Uncannily similar to a level 3 ability I gave my Frost Strider. Cold resistance and extra cold damage that ignores damage resistance. However where this cold damage is 1d4 once a turn that triggers on a hit with no action required and increases to 1d6 at level 11, mine was a bonus action to deal an extra 1d10 on the next melee attack made within the next 10 minutes that increases to 2d10 at level 11.
Hunter's Rime: Temporary hit points are always nice, especially when they trigger on an ability you were likely going to use anyways. The shutting down of disengaging is just the cherry on top of this good ability. I didn't have anything like this in my subclass.
Winter Walker Spells: I did have a feature like this, except it mostly gave homebrewed ice spells I made. My version did give Ice Knife at level 3, though. Pass without Trace, Ice Storm and Cone of Cold are good. Remove Curse should probably be replaced with a more thematic spell, though.
Fortifying Soul: Interesting. It's like a weird Song of Rest (which Bards don't even get anymore) that also gives temporary immunity to Frightened. I'm not sure I like this ability mechanically or thematically.
Chilling Retribution: Why the focus on the Frightened condition in this subclass? I'm not sure how useful this is. Rangers normally get a pretty significant damage boost at this level, and I don't think the increase in Polar Strikes die size and this ability is enough.
Frozen Haunt: Interesting, but again I don't like abilities that require you to expend two different resources to trigger. This should be worded more like "As a bonus action, which can be part of the same bonus action used to cast Hunter's Mark, you can adopt a snowy ghostly form." Becoming a wintery ghost is cool, I guess, but not the kind of thematic ability I'd give to a Ranger as a capstone. This would fit better for a Winter Druid subclass than for a Ranger, IMO.
Frozen Soul - Immunity to cold damage is situationally good, but a 15 foot emanation that deals 2d4 cold damage (which doesn't ignore damage resistance) is not good enough for a level 15 ability. This is the same area as and less damage than the Sea Druid's Wrath of the Sea.
Partially Incorporeal - This really feels like a Druid ability. Basically turning yourself into a blizzard. Not a fan. This doesn't even give you a fly speed, either.
Good idea, needs work and more thematic/mechanical cohesion. It's easily weaker than any of the Ranger subclasses in the PHB, IMO.
Scion of the Three Review:
Lore: Too setting specific for my liking. Especially when they mostly exist in a single city. And it feels like Rogues of the Dead Three should probably be Arcane Tricksters or Assassins, maybe Phantoms and Soul Knifes. Also, don't people normally dedicate themselves to only a single member of the Dead Three? It's weird that this implies that you're dedicated to all of them and switch which one you focus on on a whim. Especially when this subclass barely has anything for Myrkulites and seems to have Banites and Bhaalites more.
Bloodthirst: I actually really like this ability. The extra damage is nice, it's always good to get abilities that trigger on Bloodied. And the reaction is amazing, and limited pretty well. A Rogue with Intelligence based True Strike that focuses mostly on Intelligence to get the most out of this ability could be an interesting build.
Dread Allegiance: A pretty good ability. It won't come up often, but this is nice.
Strike Fear: Definitely worth using against powerful enemies that don't have immunity to Frightened. Pretty thematic too.
Aura of Malevolence: Hmm. Imagine 7 levels of Conquest Paladin combined with this Rogue subclass. Wouldn't be very mechanically effective (maybe if you had a Headband of Intellect), but unbelievably cool to be able to scare people to death by combining this with Aura of Conquest. Not a super strong ability, but cool.
Dread Incarnate: Both features are amazing.
I really like most of the mechanics, but think it could use some tweaks and have a bit of lore for how it could be used in other settings.