While researching monsters that can shape change to mess with my players there are a few that also have innate spellcasting. I'm trying to figure out RAW if each of the examples can use their spellcasting while using their ability to change their appearance. The wording of each's ability are all slightly different but with enough similarity that I think it can be reasonably covered in the same question.

I found the following list of creatures with both Innate Spellcasting and the Shape Change ability:

• Night Hag
• Oni
• Deva
• Some Ancient Dragons
• Smiling One Cloud Giant

Note: I'm aware not all Ancient Dragons have the Shape Change ability and that Ancient Dragons don't technically have spellcasting normally but we'll go off the assumption of using the variant rules for them in this instance as that's when it's relevant.

Night Hag

Wording of the Night Hag's Change Shape ability:

Change Shape: The hag magically polymorphs into a Small or Medium female Humanoid, or back into her true form. Her Statistics are the same in each form. Any Equipment she is wearing or carrying isn't transformed. She reverts to her true form if she dies.

Oni

The Oni has the exact same wording for their ability with the relevant pronouns swapped, clarifying what they can turn into, and a bit of extra wording to clarify that their glaive transforms with them:

Change Shape. The oni magically polymorphs into a Small or Medium humanoid, into a Large giant, or back into its true form. Other than its size, its statistics are the same in each form. The only equipment that is transformed is its glaive, which shrinks so that it can be wielded in humanoid form. If the oni dies, it reverts to its true form, and its glaive reverts to its normal size.

Smiling One

The Smiling One Cloud Giant has very similar wording with the addition of being able to transform into a beast it has seen:

Change Shape. The giant magically polymorphs into a beast or humanoid it has seen, or back into its true form. Any equipment the giant is wearing or carrying is absorbed by the new form. Its statistics, other than its size, are the same in each form. It reverts to its true form if it dies.

Devas and Dragons

Devas and Dragons seem to have extra choices on top of the basic "… magically polymorph into a …" wordings but ultimately I think the relevant portions that I'll be talking about for the wordings are all the same as above and thus for brevity I'll not copy the exact text here.

Innate Spellcasting Specifics

Almost all of the aforementioned creatures share an extremely similar Innate Spellcasting feature which includes *"…can innately cast the following spells, requiring no material components…". The only exceptions to this are the Deva which instead says it just has Verbal components for its spells (and specifically mentions retaining its ability to speak while transformed) and the Smiling One has both Innate Spellcasting feature and Spellcasting feature where it *"…has the following spells prepared…"

Common Wording Considerations

• "…magically polymorphs into…": polymorph being lowercase and none of the creatures mentioning having the Polymorph spell within their abilities makes me think this is just an innate ability of the given creature. The only real sticking point I'm unsure of for this ability is if it requires concentration or not, like if you'd cast the spell to get the effect.
• Innate Spellcasting: is well… innate. It's a property of the creature itself and not a spell being cast by it to produce the effect (though they do all include the wording "magically")
• "Statistics are the same in each form": The Night Hag, Oni, and Smiling One share this exact wording which makes me think that, as long as the form they took could still complete the required components of the spell (VSM), they'd still have the capability to cast the spell. Deva and Ancient dragons go even beyond this in that they retain some of their more powerful aspects even while transfigured and most specifically their ability to speak (talking rabbit anyone?)
• "…requiring no material components.": going off the previous statement about ability to cast the spells in question all of them allow ignoring the material component. The only slight exception to this are for the spells prepared by the Smiling One that would still require their usual components (its innate spells would still ignore the material component like the rest).

Related Questions Found

• Can a Shapechanger use Innate Spellcasting while in their animal form?: answer given was yes, they can though this is a little different as its specifically regarding the Shapechanger creature subtype (Imps and Dopplegangers being common examples), so not quite the same thing as the Shape Change ability though with similar wordings

• Does innate spellcasting by creatures have verbal or somatic components?: Answer given was essentially "requires VSM unless it explicitly says otherwise". Material is ignored for all of the innate casting but this would imply that verbal and somatic are still a requirement for each of the spells

• RAW, can innate spellcaster dragons cast spells with somatic components?: answer seems to be yes with a few other examples of creatures without "hands" still seemingly being able to innately cast spells: Faerie Dragon (tiny dragon with hand like claws), Ki-Rin (unicorn-esque creature with hooves), and Morkoth (fish creature with tentacles). This is perhaps one of the more interesting rulings as it somewhat leaves the answer up to DM interpretation but, if taken in the same context as the answer here, basically any limb likely counts for somatic components.

• Does the Shapechange spell allow one to use Innate Spellcasting of the creature they turned into?: answer seems to be Yes. The abilities described above are not the Shapechange spell but have rather similar interpretations based on how Innate Spellcasting is considered a Statistic and Special Trait and thus inherited unless specified otherwise

• Is there a way to counterspell a level 20 druid?: answer seems to be No. This is perhaps the least related but I thought it interesting enough to include. The druid's capstone feature Archdruid let's them ignore the verbal, somatic, and non-consumed material cost of spells while wild shaped. There's clearly a number of reasons this is different but it's an interesting food for thought question of if a character would recognize the somatic movement of a spell if delivered by a Ki-Rin?

My Conclusion

tl;dr: I believe the answer is Yes with some limitation based on the form chosen.

I can't find any reason, as long as the form taken can perform the required verbal or somatic components of the spell, that a creature using its Shape Change ability couldn't cast its Innate Spells. The only possible exception to this seems to be if this ability somehow required concentration though I'd expect then it would be listed explicitly in the description of the ability like how the Imp's ability to turn invisible explicitly mentions concentration. So, with that, humanoid transformations certainly could cast any innate spell and Devas and Ancient Dragons, as they retain their ability to speak, should be able to innately cast spells while transformed into… basically anything. Perhaps as long as it had a limb? So maybe not a worm though argument could be made for a certain kind of wriggling accounting for the somatic component. Note: You'd need to be extra mindful of which spells were being cast by a Smiling One for if they were innate or prepared.

Certainly DM can adjust a bit to make more interesting situations but the above appears to be RAW best I can tell.

So, did I miss anything?