We all know the general way things go. If they fight in Pure Boxing, the rules cripple the tools the MMA guy uses to win his fights. If they fight in MMA, it gives Tyson a major disadvantage against toolsets he hasn't been challenged against in his primary sport. I believe the best compromises are: 1. Kickboxing. This would hopefully put both outside their main territory. While it can be argued the kickboxing elements of MMA benefit the UFC fighter, I argue the difference of how techniques are used will be a major adaptation and neutralize the ways the UFC fighter is used to behaving. The boxer could, in theory, learn how to check leg kicks and go straight in boxing or hanging on the outside shooting jabs and ankle tap kicks. I could see Floyd doing that as his hands are good enough to beat anyone else, wait for a kick to open up a combo, and finish it. 2. Boxing, permitted clinches, punches inside the clinch, and fight in the cage so that you can tie someone on the fence. This would play into the MMA fighter's grappling expertise, but let's not forget how foolish it might be to tangle up with a boxer. You could wind up eating a lot of nasty things, and if they handtrap you, you're screwed. They would feel like it's a freestyle format where they can pull your head down into an uppercut, corner you with a clinch, etc. The UFC fighter would also have to move into the clinch without eating knuckles, and in most cases, a boxer wearing MMA gloves would be a lethal force to approach and set up a clinch with. They might even be the ones engaging the clinch. I believe the goal of said fights should be a balanced environment that neither cripples nor benefits one fighter over the other.