Hold on, one sec. Let me dig this up.....okay.
Emachina, a zetsu clone has hashirama chakra, but can't harden to take a sword to the arm or rasengan to the back from minato. They cannot regenerate... , zetsu cannot... zetsu are weak and are able to take the form of anyone they touch by copying chakra... tobi cannot.
Evidence however that shisui=tobi....
Okay. That was chapter 580, what changed so it's now a Zetsu clone?