Kaguya's other limbs are still out there.

[Your Creepy Stalker]

Black zetsu lived in Kaguya's left arm, and was essentially her entire personality.

However, it was not all of black zetsu.
Black zetsu was the size of a human back at the Valley of the End. [

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When madara put Black Zetsu on White Zetsu, there was only half a black Zetsu. [

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When Black Zetsu came from the fight with Chojuro, there was only half of that. [

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Upon possessing Obito, BZ took control of his Left arm, Just like when he lived in Kaguya's left arm.


So, clearly there are at least Two more black zetsu's out there, the right half and the Left leg. Hooray for Villains who were never properly defeated!

 

[Reboryushon]

Or he was just able to morph like the slimy creature he was..

 

[FemmeFatale]

Didn't naruto throw her arm into the moon?
Her horn is probably the only thing left, along with Madara horn thingh

 

[Six Paths]

And I actually thought that Naruto has pretty much ended as a series..

 

[Xlad]

I'm pretty sure that there is only one mind of Black Zetsu, so he just split up from his subdued body.

 

[Angelic.]

dont forget madaras legs and horns. kaguyas horn and the gedo arm. all these mysteriously disapeared from the story so its not over!

 

[Reboryushon]

And I actually thought that Naruto has pretty much ended as a series..

And it did.. People are just having a hard time getting over it.

 

[NineSNS]

Or he was just able to morph like the slimy creature he was..

This exactly.

 

[AaaaNinja]

When he covered Sasuke and Naruto at the same time, that was two Black Zetsu halves. Two halves equals a whole Black Zetsu. Have you been able to rule out that there could be a constraint to how much of a person he can cover?

 

[Hazo]

Sasuke is after BZ's half...

 

[TheFutureBest]

idk Black Ztesu I think could just transform into anything but maybe you're right