I thought Black Zarak was MegaZarak reborn?
He was, but his personality had been so neutered by Devil Zed's brainwashing that all traces of his original scheming/ambitious personality from The Headmasters were practically nonexistent.
That scar was something that the toy designers came up with. Black Zarak's smaller Headmaster form was never seen onscreen in the Masterforce cartoon. He got decapitated a few times, but the cartoon never actually treated him like a proper Headmaster. So whenever he did get decapitated, the cartoon never bothered to explain how and why he continued to survive the beheading, as if the writers simply expected the viewers to already be familiar with his toy's Headmaster gimmick without ever addressing it in the show.
You're thinking of the eyepatch. The scar wasn't part of his new look in Zone (not Battlestars), but the eyepatch was.
In the toon yes, but most of them were in other media such as comics.
I mean, there were six other Headmasters running around.
Who were all humans instead, and therefore treated the gimmick differently from how it was done in The Headmasters. The cartoon never so much as even hinted that Black Zarak was also a Headmaster. Like I said, it took a couple of in-battle beheadings to get his noggin off its body, since it never came off normally whenever he transformed. The whole "Head On!" thing that The Headmasters and Masterforce used for all their Headmasters was never done with him.