Okay...Then how would you expand their gameplay moveset, because I'm not sure myself.
Well, one thing is very clear: Dance Transformations are unique to Shantae.
So they would have their own unique magic ability, in place for transformations.
Seer Magic for Plink, Life Magic for Vera, Electro Magic for Zapple and Earth Magic for Harmony.
The first problem is trying to figure out their basic attacks.
They can't all have Hair Whips, considering some of them have hair that... Well, can't really whip well.
Plus, in Pirate's Curse, Shantae could still use her Hair Whip, even without her Genie Powers.
So the Hair Whip doesn't seem to be a Genie Power thing. And it might be unique to Shantae as well.
In that case, how would they attack?
For Vera, I can imagine using special Leaves to attack (you know the ones Shantae has in the Dance Parlor?).
But for the others... Seven Siren's gave us nothing really.
So one might need to get creative here.
Another problem is: Item Attacks
Do they all use the same items to attack as Shantae does?
(Fireballs, Pike Balls, etc.)
Or do they all use their own unique item attacks as well?
Or something different entirely?
Truth be told, I am most unsure about this one.