Gna and Hercules are about even in physical statistics, with Hercules holding a small advantage. Not to mention that his Nemean Cestus greatly amplify his physical blows and make them devastating even for beings on par with him. The stun effect specifically leaves many openings for him to get additional hits in. And his grapples would a great issue for Gna to break out of.
That said, in terms of versatility and combat mobility, Gna completely leaves him in the dust. She has a wide array of elemental attacks to use against him, not to mention her Bifrost beams, blasts and area denial waves that can explode directly on his person and bypass his blocks. Her flight allows her to avoid a lot of his attacks and she can also manifest Bifrost weapons to use.
Their stamina is pretty high, with Gna likely holding a small advantage there. And in terms of experience, Gna takes the lead what with her centuries of experience in wars with gods.
Gna should take this mid-high difficulty.
