Goo-drops are a fairly relaxed SFW closed species and extra traits are not rarity bound, but they must be safe for work and not hateful(racist, ableist, etc).
For something to be a goo-drop it must have the following traits:
1. a clear container neck and ventral side (belly) filled with a gooey substance and at least one awakening item
- 1a. Ray-Drops must have their awakening item in their capsule tail, not in their belly.
2. an opaque dorsal side (back) or a dorsal side with opaque elements incorporated
- 2a. Goo-droplets must have a opaque pointy hat since they don't have a normal dorsal side
3. at least 2 legs that must be opaque (including prosthetic limbs) or with opaque elements incorporated
4. a tail of some kind
- 4a. Goo-droplets don't need a tail and usually don't
5. an opaque (or with opaque elements incorporated) mask like face
6. Goo-drops must be fat/round.
- 6a. Goo-wyrms, while longer than the other types of goo-drops, must be a thick noodle shape. They cannot be skinny, think pool noodle not spagetti noodle.
and that's it!
Addendum
While anthro/gijinkas goo-drops are not cannon, since they are exclusivily a feral species, you are free to make an anthro/gijinka version of your goo-drop. I would personally recomend keeping the character fat. That being said I can't stop you doing otherwise since that character is now an alternate universe version of the character and isn't limited by the species traits anymore.
Still, keep the character SFW and non hateful please.