Yeah IDK about that, I don’t think you can act a fake fight convincingly without having at least some actual skill. The moves they use are always derived from actual martial arts, the only difference is that your partner knows ahead of time what’s going to happen and how to react, and you don’t hit them to hurt. But I’m pretty sure you could figure that part out pretty easily if push comes to shove.
As long as he’s fighting an untrained opponent who’s shorter than him, my money would be on Mamoa. And even if he’s trained I’d still bet on him unless we’re talking about one of the Gracie’s.