Hi friends!

I'm working on writing and building a homebrew world of my very own, and I've decided that it will have a lot of cosmic influence. I like the aesthetic of it and I think it could make for some inspired world-building, but I need some help! At least until I get my hands on a copy of Stargazer's Guide to Aroria.

If you were to design a special Starry Form (a la the Circle of Stars subclass) for each of the 12 zodiac signs we all are familiar with? I want the main arcane council of this world to have some extra-celestial goodness to them, and I think an individual Starry Form for each of them would be fun and make for some interesting mechanical implications. Let's  brainstorm!

EDIT: I'm not looking to add these forms to the existing ones in the Circle of Stars subclass. I wanted to give each of these twelve NPC's their own unique character feature based on the zodiac sign they represent, so they'll be singular features rather than a huge list that a PC would have to choose from. Sorry for the confusion!

I am a Pisces, so lets start there. A quick wikipedia search reveals the following details surrounding its mythology: 

 A basic wildshape (at certain levels) will already let you transform into a fish, so thats not a very interesting use of the starry form. But perhaps focusing on the idea of "escape" and that pisces is usually represented as a pair of fish. I am thinking something similar to the Mirror Image spell, but with only one duplicate.

Pisces: A constellation of of twin fish appears on you. You gain a swim speed equal to your walking speed. As an action on a subsequent turn while this form is active, you can summon an illusory duplicate of yourself in your space The duplicate moves with you, and appears to mirror your actions. When a creature makes an attack against you, it must make a Wisdom saving throw against your spell save DC. On a failed save, the creature hits the duplicate instead, which vanishes and is destroyed. A creature with blindsight or truesight automatically succeeds on its saving throw. The duplicate vanishes early if your Starry Form ends. Once the duplicate vanishes, it cannot be summoned until you use this form again. 

10th level Improvement - Duplicate can take up to 3 hits before vanishing. 

Aries: A constellation in the form of a ram appears on you. When you activate this form, and as a bonus action on each of your subsequent turns while it lasts, you can make a melee spell attack against a creature within your reach. On a hit, the creature takes force damage equal to 1d8+you Wisdom modifier and must make a Strength saving throw against your spell save DC. On a failed save, the creature is shoved up to 10 feet away from you. Additionally, for the duration whenever you make an Athletics skill check to break an object, you can use your Wisdom modifier in place of Strength. 

10th level improvement - Damage increases to 2d8 and a creature which fails its save is knocked prone in addition to being shoved

Taurus: A constellation in the form of a bull appears on you. While this form is active, you have advantage on all ability checks and saving throws to resist being knocked prone or moved against your will. 

10th level improvement - While active, you automatically succeed on ability checks and saving throws to resist being knocked prone or moved against your will

Gemini: A constellation which appears like a starry version of yourself appears on you. An ethereal duplicate of yourself appears in your space and aids you in completing more tasks. On each of your subsequent turns while this form lasts, after you take the Cast a Spell action on your turn you can use your bonus action to either take the Help action or make a single weapon attack. 

10th level improvement - The creature aided by a Help action you take as a bonus action gains a bonus to their roll equal to your Wisdom modifier. If you make a weapon attack as a bonus action, on a hit you gain a bonus to the damage roll equal to your Wisdom modifier and the attack counts as magical for overcoming resistances. 

I would also say a couple of them could just be reflavored to match the original options

Sagittarius = Archer

Aquarius = Chalice

As a side note, if you are going to introduce 12 more star forms for the Circle of Stars druid, it may also be a good idea to introduce a house rule restriction on the Starry Form feature to limit the number of star forms the druid has access to at any given time. Having all 15 options available at level 2 adds way too much versatility to the feature

I love all of these suggestions! And I was planning on making these new forms a special feature for each member of the arcane council, rather than adding them to the existing forms that already exist within the subclass, but if I decide to change my mind on that, I'll take that to heart.

Cancer: "A crab-like constellation appears upon your person, complete with pincers or claws. You are able to grapple a target within 10ft of you as a bonus action."

Libra: "The form of a celestial scale manifests upon you, granting you the ability to balance fortunes. When a creature you can see within 60ft of you has advantage or disadvantage on their roll, you may use your reaction to nullify that advantage or disadvantage, treating the roll as normal.

Scorpio: "The constellation of a scorpion, complete with a fearsome stinger, shines upon you. When you successfully strike an opponent with an attack roll, that target must then make a Constitution-saving throw. Upon a failure, the target's movement speed is reduced to 0 until the end of their next turn.

Ophiucus: "The image of a glinting viper coils around your person. Attack rolls against you have disadvantage, and your melee attacks rolls & touch spells have their range doubled for the duration.

It's a cool idea. Maybe each Sign gives you some small benefit once per short rest. BUT... having access to twelve forms is a bit to powerful a low levels. So maybe when you choose that Circle at level 2 you have access to one maybe two of the signs. And then maybe every two levels thereafter you get to learn one additional sign. And maybe you have to go somewhere and perform some specific ritual under the night sky during a certain phase of that constellation's zenith in order to petition the cosmos for access to that sign's gifts. That would incorporate a nice bit of role-playing into the mechanics. 

Also - maybe the gifts of each sign are only available to you during that sign's month of the year or something. 

Anyhow. As far as the abilities, each sign grants a general gift and a specific gift. The general gifts are damage resistances. Each sign is associated with an element - earth, air, fire, or water. So when a sign is active on you, you have resistance to that form of damage - bludgeoning, thunder, fire, or cold. (Which sign is which element? I honestly don't know, you'd have to google that.) I think this damage resistance thing is a good thing to set as the Level 6 ability. 

So at the end of each short or long rest you choose which resistance you want to activate based on which signs you have access to. And maybe at Level 10 or maybe Level 14 that resistance gets shared by all allies who are within a certain distance of you (say maybe 30 ft). 

As for the specific gifts... well, that gets a lot more complicated, because there's 12 of them. 

I'll get back to you on that.