Completely RAW, Balanced, and Unconventional Races (Spheres)

[SangoProduction]

(Eternal) Transformation feat + Human = just about any creature you can think of. Single best General talent in the game, not for power, but for granting you every single creature as a playable race, without breaking the game, enforcing dumpster diving, nor taking a ship ton of time. (And the Eternal version does nothing but commit to the bit, and say "no, you don't actually have a human form to fall back on.)

Want a Dragon? Dragon Transformation (I like the term Genotype used in 5e version, which I'll just shorten to Gene). Obviously. You get the basic shape, and abilities associated with your form, like breath weapon, that scales on character level.
Although you'd have to wait until you get Improved Transformation to give it gliding / flight. You're just a hatchling for now.

Giant Spiders, Snakes and Dogs? Obviously, they have their own specific genes.
Mimics? Similarly have an Object gene.
Beholders or Gelatinous Ooze or Black Sludge, or Living Freaking Fire? Not a problem.
And this isn't even being particularly creative with any of them.

Now, for specific abilities, or certain capabilities, the simple Transformation feat will not grant you it.

So, if you are a Werewolf, or Troll, you will still have to get access to the Life sphere with the Regenerate drawback to get your fast healing / regeneration. (But you can be big, green, and, and take Giant's Fortitude trait for a regenerating pool of temporary hit points, with your Anthropomorphic Gene.)
Basilisks would want to invest in Destruction sphere with Crystal Blast (covers the target in rock, leaving them immobile, until they break free). Not nearly as lethal as a default basilisk's instant petrification on a failed save, but usable in a normal party.
And if you want your Psicrystal to be mobile, you probably want to take the Wraith class with the Matagot archetype. (Honestly, a reasonable DM would just let you reflavor Matagot by default, But if they don't, Transformation is still an option available to you.) (Also, Elemental Transformation doesn't remove your ability to move. But I always have to throw out "You get to be a familiar," whenever I can gush about it.)

Can you be a Ham and Cheese Sandwich? No. But you can be much more evil and disgusting as a Soy-substitute Ham and Cheese Sandwich. (Take Death sphere.)
You can all be household appliances, and go on an adventure, like in that movie... from the 90s I think.

[pabelfly]

(Eternal) Transformation feat + Human = just about any creature you can think of. Single best General talent in the game, not for power, but for granting you every single creature as a playable race, without breaking the game, enforcing dumpster diving, nor taking a ship ton of time. (And the Eternal version does nothing but commit to the bit, and say "no, you don't actually have a human form to fall back on.

So, for context (I haven't really delved into Spheres), how much build resources does this take to get?

And what sort of limits are placed on what you can select? Is there any cap on base stats you can have with your new form, how many limbs or attacks it gets, or what racial abilities you can get with it?

[SangoProduction]

So, for context (I haven't really delved into Spheres), how much build resources does this take to get?

And what sort of limits are placed on what you can select? Is there any cap on base stats you can have with your new form, how many limbs or attacks it gets, or what racial abilities you can get with it?

http://spheresofpower.wikidot.com/alteration#toc41
It takes just one feat, the Transformation feat. You get to select any of the (transformation) talents. The limbs and speed are define, as well as any natural armor or weapons. You also gain any abilities under Special, given that it's not saying you spend spell points.
You get to select no "traits" unless you pick up Improved Transformation (Or choose Anthropomorphic Transformation, since that's part of their Special, designation). And some of the forms don't grant speech (which is not a thing in the 5e version - they realized their mistake), which is probably going to be a problem unless you take Hybrid Transformation to "retain" those capabilities from your base human form.
You do not get additional stat points. (Exception to if you get the Size Change trait, which grants +/- 2 to strength / dexterity, depending on whether you go small or large).

To emulate additional abilities that are iconic beyond the base aesthetic form requires slightly more effort. And is sometimes functionally impossible within the context of purely using Spheres - like dragons getting racial vancian casting - but you can just... take this feat, and go normal sorcerer to emulate that, and the Behir has 12 legs, which is functionally impossible to explicitly replicate but does it have functionality of more than 6 legs in any realistic situation? Probably not.

But the biggest deal is that you are aesthetically any creature, and if you're replicating a powerful type of creature, you put more build resources into becoming more like them as you level up. But you aren't "trapped" in racial levels. And you don't "have" to take every mostly worthless racial trait of a given creature, like Savage Species does with like 50 more pages of rules.

[pabelfly]

http://spheresofpower.wikidot.com/alteration#toc41
It takes just one feat, the Transformation feat. You get to select any of the (transformation) talents. The limbs and speed are define, as well as any natural armor or weapons. You also gain any abilities under Special, given that it's not saying you spend spell points.
You get to select no "traits" unless you pick up Improved Transformation (Or choose Anthropomorphic Transformation, since that's part of their Special, designation). And some of the forms don't grant speech (which is not a thing in the 5e version - they realized their mistake), which is probably going to be a problem unless you take Hybrid Transformation to "retain" those capabilities from your base human form.
You do not get additional stat points. (Exception to if you get the Size Change trait, which grants +/- 2 to strength / dexterity, depending on whether you go small or large).

To emulate additional abilities that are iconic beyond the base aesthetic form requires slightly more effort. And is sometimes functionally impossible within the context of purely using Spheres - like dragons getting racial vancian casting - but you can just... take this feat, and go normal sorcerer to emulate that, and the Behir has 12 legs, which is functionally impossible to explicitly replicate but does it have functionality of more than 6 legs in any realistic situation? Probably not.

But the biggest deal is that you are aesthetically any creature, and if you're replicating a powerful type of creature, you put more build resources into becoming more like them as you level up. But you aren't "trapped" in racial levels. And you don't "have" to take every mostly worthless racial trait of a given creature, like Savage Species does with like 50 more pages of rules.

Ah, okay. Thanks for the response.