Written in the Stars
Welcome to a subclass where starlight empowers you, where gazing at the night sky for hours on end is wholeheartedly encouraged, and where Druids can be best friends with Great Old One Warlocks! It's the Circle of Stars Druid!
This definitely falls under the category of things I wouldn't have thought to have associated with a Druid – but just because I was surprised by the theme of the subclass doesn't mean it doesn't make sense for the class. I feel like this is a piece of the puzzle we didn't know we were missing, and a very cool and strongly flavourful one at that.
The subclass features below have short summaries of the rules they relate to. You can download the full rules for this subclass for free from the Wizards of the Coast website, here.
Star Map - 2nd Level
Your spellcasting focus is a star map of a description of your choosing. You can use it to cast Guiding Bolt or Augury a number of times in total equal to your Wisdom modifier. (e.g. Wisdom modifier of +3 allows 2 Guiding Bolts and an Augury, or 3 Guiding Bolts, or 3 Auguries etc.)
Introduced by a colourful twist on your spellcasting focus which really points you towards any number of interesting lines of roleplay, this feature then follows up with the ability to cast spells for free. That was the secret hiding in the stars all this time. FOR FREE. As your journey through the ranks of the Druids progresses, you'll have up to 5 chances to cast Guiding Bolt or Augury without expending a spell slot or having to prepare them (neither one is a Druid spell but this is just reinforcing the fact that they are FREE.)
Before the inevitable thought enters your head (“yes, but Guiding Bolt at 1st level isn't very powerful and you can't upcast it with this feature) let's not forget that being able to deal damage and give someone else advantage at lower levels is definitely not too shabby. As you reach the heady heights of Druid-dom (Druidity? Druidiocy?) you'll still have five free Augury casts that you can really annoy your DM with (your cantrips will be more powerful than a Level 1 Guiding Bolt at this point, unless you're desperate to give someone advantage on their next attack... like, say a ROGUE cough). Plus, making them say weal or woe is fun. Like a little mini-game, if you will. Did I mention those spells are FREE?
Starry Form - 2nd Level
Expend a use of your Wild Shape. For 10 minutes you look like a constellation and shed light up to 20 feet.
Looking like a constellation and shedding light up to 20 feet (10 feet of bright light, 10 feet of dim light) will of course make you the centre of attention at a rave. Being as that seems like a fringe benefit in the realm of fantasy roleplaying (depending on your DM of course, and it's obviously vital if you're involved in a Sci-Fi campaign), you get the following benefits depending on which of three possible modes you choose.
Chalice
Heal yourself or another creature within 30 feet 1d8+half your Druid level HP when you use cast a spell (that uses a spell slot) to heal.
Upgrade your heals to multi-target for free at 2nd level to flip the bird at the Life Cleric.
Archer
As a bonus action, you can make a 60 foot ranged attack that deals 1d8+Wisdom modifier damage.
The latest in a line of features to flip the bird at the Ranger.
Dragon
If you roll a 9 or lower on the die for an Intelligence or Wisdom check or a Constitution save to maintain concentration, count that die roll as a 10 instead.
I was expecting some kind of breath weapon attack, but dragons are indeed wise. This potentially has some useful input in a build that revolves around casting concentration spells (which we will definitely look at if the class becomes official). In particular, it has use at higher levels (not losing concentration when you cast something like Sunbeam for example – you want to get your money's worth out of a 6th level slot!). I've mentioned a couple of times in these Unearthed Arcana reviews that it's always good to see things that encourage classes to be played in different ways, and this opens the door for Druids to be more than just heal bots or angry bears (or elementals).
Cosmic Omen - 6th Level
When you finish a long rest, roll a die. You can use a reaction to affect Ability Checks, Saving Throws and Attack Rolls depending on whether you roll odds or evens. This feature can be used a number of times per long rest equal to your Wisdom modifier.
- Odds: Roll a d6 and deduct the number rolled from the chosen roll.
- Evens: Roll a d6 and add the number rolled to the chosen roll.
Checking the stars for omens. You might find your best pal, the Great Old One Warlock sat next to you doing the same thing, staring at you lovingly, or ranting in a strange and barely intelligible language, frothing at the mouth...
The feature is pretty useful, though – everyone enjoys this kind of thing in a Divination Wizard's arsenal (and Bardic Inspiration, of course) and having some kind of control over the flow of fate is always going to be helpful. Or at least reassuring up until you roll that 1 you just didn't want to see!
Full of Stars - 10th Level
You are resistant to bludgeoning, piercing and slashing damage while your Starry Form is active.
Flavour wise, yes, this is definitely interesting and makes a lot of sense. However, much as having resistance to these particular things might seem like you should go skipping into the fight to tank the boss, maybe think carefully before you do. It's quite a lot different to a Druid's go-to for being rough and tough – Wild Shape gives you a big stock of Temporary HP, after all. Resistance will effectively double your health pool for 10 minutes but, depending on your level and how you've built your character, that may not be quite as effective as turning into a huge, angry beastie!
Star Flare - 14th Level
Create a 30 foot radius sphere of intense starlight. Teleport any willing creatures inside it up to 30 feet away from it. All creatures remaining in it must pass a Constitution save or take 4d10 radiant damage and be blinded.
It's also worth mentioning that this can be reused if you're willing to sacrifice a spell slot of 5th level or higher, which gives you a multiple use area of effect “spell” (it doesn't count as a spell when used) that comes with free battlefield control tacked on as a special offer. You should be aware that 4d10 damage is not reliably huge, but the blindness effect is rather nice – between this and the ability to cast free Guiding Bolts with your Star Map, Rogues will definitely love you.
Conclusion
All things considered, this class seems very reasonable. Druid builds allow for a good deal of versatility, and choosing this subclass would open up paths that other more spellcaster-y druids don't necessarily walk (e.g. Circle of the Land), particularly with its ability to affect Concentration saving throws through two different features from level 10. The surrogate Wild Shape that is Starry Form is interesting as well, and allows for consistent multi-target healing during combat, which is always a help! With several ways to create advantage for the rest of your party, you'll find that this subclass does pretty well in a support role, too.
Still, my favourite thing about the Circle of Stars is probably how strongly flavourful it is, and how cool it is to see this kind of lore head in the direction of Druids. Give this one a go – it might just Yog your Soths Oth!
Shout out to The Shropshire Dungeon Master for making me realise that the Chalice option for Starry Form is more of a big deal than just a "'Nuff Said"! If Shropshire is too far away for you then you can also find him on Twitch!