Okay. Let's just give baseline points for Beheaded.
1. Forcefields are less of an issue for Beheaded than characters like Neo. The issue is that they constantly regenerate- however Beheaded's tactics are explicitly that he is attacking from many, many fronts, and it isn't just himself- his summons, traps, and turrets are additionally assisting, and his own attacks can function over each other, such as multiple grenades all at once.
2. If falling off is literally a win condition, and Beheaded would be familiar with that strategy, then he has another advantage here- the magnet grenade can just pull Han off and send him into the abyss below, effectively BFRing him. Han seems to lack flight in this key.
3. AP advantage is ridiculous. If Beheaded lands even a single strike on Han's actual body, Han is paste irrevocably. Furthermore, Beheaded is immune to projectiles (not physical strikes, don't ask me why it is very specific) up to his own level so any ranged attacks go straight out the window. Han has nothing as strong as Beheaded's raw AP. Furthermore, Beheaded can heal and become invulnerable to damage during that, too. For reference, he has 13x over Han's actual form.
4. A single resurrection could be pivotal. I hadn't brought it up in past threads since I doubt it was needed, none of them could take down Beheaded. However here it might be relevant. Once reaching death and only once, Beheaded will rise again to maximum health and continue fighting.
5. Obviously the age-old typical Beheaded strategies. If a weapon strikes his shield, that weapon is now gold coins. He's absolutely going to try to cover the entire battlefield in effects of some kind, be it ice-arrow firing turrets, balls of death energy, electric bolts, small tornadoes to shift around everything, etc. Beheaded's strategy is l o t s.
6. Some powers of Han's will flat out not work on Beheaded purely due to his status as what is functionally a corpse ragdoll possessed by a handful of sentient cells. Draining the life force from a corpse, for example, just is flat out a no. And a big part of why this is pivotal is that Han may try to do that- thus wasting even the briefest of seconds on his part.
7. Han abusing range advantage on a tiny arena is the worst point I have ever heard. Both of them have enough range to account for the entire arena so Han will not be abusing range any time soon unless he enjoys walking off into the abyss and killing himself.
8. Attack reflection. Beheaded already does not need to worry about Han's barrage of arrows since they just flat out cannot hurt him. But reflecting explosions and stuff back at Han? Now that's a strategy I can get behind.
9. Tethers, while a weird point, isn't valid for the guy that has fought the tentacle monster.
10. Pretty sure we established Han don't use no dirty damn BFR. Since it was brought up before and all. Just sayin'.
I vote for Beheaded, high-diff. The forcefields are the worst issue but Beheaded's raw versatility and huge AP advantage handle other obstacles relatively well. Even with Han's damage reduction he's still got the AP to one-shot, plus all of his other attacks are constantly harming Han as well. I'd point out that Beheaded's traps have similar AP and durability to himself. The summons are questionable since they're a horde of smaller creatures but collectively they have the same AP as well.