Made in Hong Kong Skeletor has a hard head. As far as I know, there are three types that are fairly similar, however, they each come with different stamps: Mattel. Inc. 1981 , Mattel. Inc. 1983 and I think one has "Hong Kong".
The armour and weapons should be stamped with "Hong Kong" and are a darker purple. I have not seen any HK accessories for Skeletor that are not marked with Hong Kong?