Thanks for all the input! It was very helpfully.
Here's a rough look at what I've come up with. Disclaimer: My group is pretty casual, so I'm not too worried about optimization, and I don't realistically think this game will go past Level 7-8, so I didn't bother to map out higher level features.
This hack is meant to work as a druid subclass that echoes Circle of the Moon, so the CR's and power levels of wildshapes are meant to roughly fall into place with what a Moon Circle druid could do. Also, since these druids will be using their own HP instead of the creature's HP, I'm being less strict with the CR values. To make up for
not getting to use a creature's HP, I'm giving the druid some Temporary HP each time they wildshape.
For Beast Forms, I'm going to craft some templates (in the spirit of Conjure Beast, Find Steed, as per the suggestion above from
@Quickleaf), rather than use monster stat-blocks. As we all know, the beast stat blocks are all over the place in terms of capability and are fairly limited, so I want to bring both versatility and parity to them... they're still a work in progress.
Lingering questions:
-Are the temp hp values I assigned for wildshapes fair? Too high? Too low?
-Since I'm stealing the class' core feature, Wildshape, should there be a replacement? Maybe something like the 1D&D's Channel Nature feature?
Everything is still subject to change, so let me know if anyone sees any egregious flaws with my plan...
CIRCLE OF THE WILD FLURRY
Wild Flurry Spell Shaping (Level 2)
At Level 2, when you take this circle, your Wildshape class feature becomes integrated with your spell slots and is replaced with the following Ritual and Spells:
You gain the following Ritual:
Form of the Harmless Spy
Casting Time: 1 minute (Ritual)
Range: Self
Components: S
Duration: 1 hour, concentration
You assume the shape of a small or tiny beast that you have seen before. The beast has a CR of 0. You retain your own Hit Points and Hit Dice while in this form, but all other normal rules for Wildshape apply.
And you gain the following Spell, which is always Prepared.
Wildspell Beast Shapes
Casting Time: 1 bonus action
Range: Self
Components: S
Duration: 1 hour
You assume the shape of a beast that you have seen before. The statistics of this form are based on one of the following templates: Skirmisher, Brute, Swift, Aquatic, or Aerial
You retain your own Hit Points and Hit Dice while in this form, but all other normal rules for Wildshape apply. You can end this spell as a Bonus Action, reverting you back to your normal form.
When you cast this spell you gain 8 temporary hit points, which last for the duration of the spell.
At Higher Levels: The duration of the spell increase by 1 hour, the statistics of your form increase (as per template) and you gain an additional +4 temporary HP.
Note on Templates:
Cast at Level 1, the Templates should be similar in power to a CR ½ Beast. Cast at Level 2, CR 1; Cast at Level 3 CR 2, etc. Templates will not have multiattacks until cast at Level 3 or higher.
Skirmishers = Emphasize speed and attacks, with potential features like Ambush Predator, Pack Tactics, Pounce, or potentially even poisons.
Brute = Emphasize strength and heavy attacks, more temp HP. Potential features may include grapples, slows, and ‘sentinel’ reactions
Swift = Built purely for running fast. Weak attacks. Might have potential features for minimizing Opportunity Attacks or something like “evasion” or “uncanny dodge”
Aquatic = Built for being in the water, but not very effective on land
Aerial = You can fly, but will have less combat power than a Brute or Skirmisher.
Monstrous Spell Shaping (Level 6)
At level 6, all of your Wildshape form attacks count as magical for purposes of overcoming resistances and immunities.
Wildspell Monstrous Shapes
Casting Time: 1 bonus action
Range: Self
Components: S
Duration: 1 hour
You assume the shape of an “beast-like” Monstrosity, Fey, Celestial or Fiend that you have studied, subject to DM Approval, with a CR no greater than 2.
You retain your own Hit Points and Hit Dice while in this form, but all other normal rules for Wildshape apply. You can end this spell as a Bonus Action, reverting you back to your normal form.
When you cast this spell you gain temporary hit points equal to its Constitution Score, which last for the duration of the spell.
At Higher Levels: Increase the CR of potential shapes by 1.
Elemental Spell Shaping at Level 10? TBD??