Board Thread:New on Ben 10 Wiki/@comment-37390956-20181110111416/@comment-32133544-20181117045953

Zs'Skayr cannot appear in Reboot because
 * Ben does not have Ghostfreak.
 * Even if he would be alive, why would he come to Earth and become a villain? He is the king on his planet where he can get all the things he needs. So, there is no need to come to Earth.

Vulkanus may appear but he would be defeated by Ben easily.

Even Albedo cannot appear because Ben neither met Azmuth nor he knows much about Omnitrix.

I personally think Kevin Levin should appear in Reboot.