What happen to Yamato
This is just my theory.
Kabuto captured Yamato during his (& Deidara) attacked on the "island".
Kabuto than added Yamato (with Hashimara DNA) to upgrade Madara.
This was how Madara had 'Hashimara' face on Madara body.
Orochimaru using Hashimara DNA to create; as only Yamato was successful.
He told Madara 'in-directly' that he had upgraded Madara with 'something special' for power boost.
Madara then test the upgrade by creating the forest, trees, sky; etc.
The zetsu had nothing to do with Kabuto (& Yamato).
Madara already created zetsu by means of parasite by himself.
This is just my theory.
Kabuto captured Yamato during his (& Deidara) attacked on the "island".
Kabuto than added Yamato (with Hashimara DNA) to upgrade Madara.
This was how Madara had 'Hashimara' face on Madara body.
Orochimaru using Hashimara DNA to create; as only Yamato was successful.
He told Madara 'in-directly' that he had upgraded Madara with 'something special' for power boost.
Madara then test the upgrade by creating the forest, trees, sky; etc.
The zetsu had nothing to do with Kabuto (& Yamato).
Madara already created zetsu by means of parasite by himself.