I found this version on the Xena d20 page.
Pankration (General)
You are trained in a particularly brutal form of wrestling.
Prerequisites: Improved Unarmed Strike, Improved Grapple.
Benefit: If you start your turn grappling, you get an additional attack at your highest attack bonus. This action can be used to attack an opponent with an unarmed strike, natural attack or light weapon, damage your opponent, pin or break a pin, use the opponents weapon or doing any other attack action that is possible while grappling.
Hope this helps.